47 Extravascular fluids

Lothar Thomas

47.1 Ascites

47.1.1 Biochemistry and physiology

The peritoneum approximates body-surface area in size. Anatomically the peritoneum is composed of:

• The visceral layer that accounts for 80% of the total surface area
• The parietal layer, which lines the undersurface of the diaphragm and the interior surface of the abdominal wall
• The peritoneal cavity. Both layers are separated by a thin layer of peritoneal fluid that is produced by the ultrafiltration of plasma (peritoneal cavity).

Ascites is the pathological accumulation of fluid within the peritoneal cavity. The word ascites is of Greek origin and means bag, bladder, or belly. Ascites is defined as more than 25 mL fluid in the peritoneal cavity. Smaller volumes of fluid (as little as 50 mL) can be detected using radiological methods or ultrasound while larger volumes (500–1,500 mL) can be detected by percussion. Ascites can occur at any age, including in utero. It is most commonly caused by liver cirrhosis in adults and by hepatic or renal disease in children /1/.

In the liver blood flows from the hepatic artery and portal veins via the hepatic sinusoids and leaves the liver via the hepatic veins to the inferior vena cava. The sinusoidal pressure is approximately 2 mmHg because resistance to afferent flow is significantly greater than the efferent resistance. Hepatic lymph is formed by the filtration of sinusoidal plasma into the space of Disse. Every day, 800–1,000 mL are drained from the liver via the trans diaphragmatic lymphatic vessels to the thoracic duct, from where it enters the left subclavian vein. Because the hepatic sinusoidal epithelium is highly permeable to albumin, the total protein and albumin concentration in the hepatic lymph is comparable to that of plasma. There is no significant osmotic gradient across the sinusoidal membrane

In the small intestine, blood from the mesenteric capillaries drains via the mesenteric veins into the portal vein. The mesenteric capillary pressure is approximately 20 mmHg. Intestinal lymph drains from regional lymphatic vessels and combines with hepatic lymph in the thoracic duct. In contrast to the hepatic sinusoidal endothelium, the mesenteric capillary membrane is relatively impermeable to albumin, so the total protein concentration in the mesenteric lymph is only 20% of that in plasma. This creates a significant osmotic gradient that facilitates the return of interstitial fluid into the capillaries /1/.

In portal hypertension, ascites develops when hydrostatic and osmotic pressures within the hepatic and mesenteric capillaries produce a net transfer of fluid from the blood vessel to the lymphatics at a rate that exceeds the drainage capacity of the lymphatic vessels.

In most cases of cirrhotic ascites, the protein concentration of the ascitic fluid more closely resembles intestinal lymph than hepatic lymph. This suggests that hepatic fibrosis progresses to cirrhosis, there is decreased capacity for lymph formation by the liver, and that the majority of cirrhotic ascites may be of splanchnic origin /1/. The normal hepatosplanchnic lymph formation is about 1 mL per minute. In patients with cirrhosis, this can be as high as 10 mL per minute.

Ascites signifies a deterioration of renal and circulatory function. Patients with ascites have a positive Na⁺ balance i.e., Na⁺ excretion is low relative to Na⁺ intake. They are also at risk of developing severe hyponatremia and hepatorenal syndrome, which together with spontaneous peritonitis represent significant clinical and treatment challenges /2/.

47.1.2 Cirrhotic ascites

Three main pathological processes are responsible for the development of ascites:

• Portal hypertension increases the hydrostatic pressure gradient in the splanchnic vessels resulting in elevated intestinal lymph formation. Ascites occurs when lymph formation exceeds the lymphatic drainage capacity and accumulates in the peritoneal cavity /1/. In patients with cirrhosis the rate of lymph formation can increase up to 10 mL/min. /3/. The topography of the liver injury is an important factor in the treatment of ascites. Patients with post hepatic portal hypertension due to hepatic vein thrombosis (Budd-Chiari syndrome, for example) are difficult to treat whereas patients with ascites due to portal vein thrombosis respond well to treatment.
• Systemic and splanchnic nitric oxide mediated peripheral vasodilation results in a decline in the effective arterial blood volume and a hyperdynamic circulation causing hypovolemia /2/.
• Hyperaldosteronism: the effective hypovolemia in patients with ascites is sensed by the renal juxtaglomerular apparatus of the kidney. The kidney responds (i) with stimulated renin-angiotensin-aldosterone system leading to increased sympathetic activity, and (ii) with elevated secretion of antidiuretic hormone (ADH). The ADH increase promotes free water retention and expansion of the plasma volume. In cirrhosis the vasoconstrictive effects of angiotensin are blunted, allowing perpetuation of systemic arteriolar vasodilation of the splanchnic bed and systemic vascular steal and continued systemic under filling /1/.

47.1.3 Etiology of ascites

Liver cirrhosis is the main cause of ascites in Europe and North America, accounting for 80% of cases. Approximately 50% of patients with compensated cirrhosis develop ascites within 10 years and half of these die within 2 years of developing ascites. Mortality from cirrhosis is 12.7 per 100.000 and 10–20% of those with one of the three most common liver diseases (non alcoholic fatty liver disease, alcoholic liver disease, and chronic hepatitis C) develop cirrhosis over a period of 10–20 years according to a study in the UK /4/.

Malignant disease is the second most common cause, accounting for 10% of cases, followed by heart failure and a range of other diseases (Tab. 47.1-1 – Types of ascites). A small proportion of patients with ascites caused by advanced cirrhosis also develops hepatic nephropathy, which carries a poor prognosis /2/.

47.1.4 Definitions

Terms defined by the International Ascites Club.

Uncomplicated ascites

Ascites that is not infected and which is not associated with the development of hepatorenal syndrome.

Ascites can be graded as follows /3/:

• Grade 1 (mild): ascites only detectable by ultrasound examination
• Grade 2 (moderate): ascites causing moderate symmetrical distension of the abdomen
• Grade 3 (large): ascites causing marked abdominal distension.

Refractory ascites

Ascites that cannot be mobilized or early recurrence of which (that is, after therapeutic paracentesis) cannot be satisfactorily prevented by medical therapy. This includes the following subgroups /3/:

• Diuretic resistant ascites (is refractory to dietary sodium restriction and intensive diuretic treatment)
• Diuretic intractable ascites (ascites that is refractory to therapy due to the development of diuretic induced complications that preclude the use of an effective diuretic dosage).

In approximately 5% of patients with ascites, more than one cause is responsible. This is known as “mixed” ascites. Usually, these patients have cirrhosis plus one other cause such as peritoneal carcinomatosis or tuberculous peritonitis.

47.1.5 Differentiation of ascites

The first stage in the differentiation of ascites is visual inspection of the ascitic fluid (Tab. 47.1-2 – Appearance of ascitic fluid and diagnostic comment). The choice of tests depends on the clinical presentation. Routine investigations are sufficient in cases of uncomplicated ascites due to portal hypertension where the ascitic fluid is straw colored and clear.

If infection is present or the ascitic fluid is turbid or pseudo chylous, further investigation may be required. Some tests are rarely necessary and many others that are still in use are often pointless /3, 4/ (Tab. 47.1-3 – Laboratory determinations in ascites according to AASLD practice guidelines).

One of the most important investigations used to distinguish cirrhotic ascites from other forms is the serum-ascites albumin gradient (SAAG). Its importance in the differential diagnosis of ascites is shown in Tab. 47.1-4 – Assessment of serum-ascites albumin gradient (SAAG). The assessment of laboratory test results of ascites is summarized in Tab. 47.1-5 – Assessment of laboratory test results in different types of ascites.

The exudate-transudate concept, which is based on the total protein concentration, can lead to misclassification. This is why the concept is no longer recommended by the American Association for the Study of Liver Diseases (AASLD) and the British Guidelines on the Management of Ascites in Cirrhosis /3, 4/.

References

1. Giefer MJ, Murray KF, Colletti RB. Pathophysiology, diagnosis, and management of pediatric ascites. JPGN 2011; 52: 503–13.

2. Pedersen JS, Bendtsen F, Moller S. Management of cirrhotic disease. Ther Adv Chronic Dis 2015; 6: 124–37.

3. Moller S, Henriksen JH, Bendtsen F. Ascites: pathogenesis and therapeutic principles. Scand J Gastroenterol 2009; 44: 902–11.

4. Moore KP, Aithal GP. Guidelines on the management of ascites in cirrhosis. Gut 2006; 55 suppl VI: vi1–vi12.

5. Runyon B. Management of adult patients with ascites due to cirrhosis: an update. Hepatology 2009; 49: 2087–107.

6. Piso P, Arnold D. Multimodale Therapiekonzepte der Peritonealkarzinose bei kolorektalen Karzinomen. Dtsch Ärztebl Int 2011; 108: 802–8.

7. Tarn AC, Lapworth R. Biochemical analysis of ascitic (peritoneal) fluid: what should we measure? Ann Clin Biochem 2010; 47: 397–407.

8. Runyon BA. Amylase levels in ascitic fluid. J Clin Gastroenterol 1987; 9: 172–4.

9. Akriviadis EA, Runyon BA. Utility of an algorithm in differentiating spontaneous from secondary bacterial peritonitis. Gastroenterology 1990; 98: 127–33.

10. Steinemann DC, Dindo D, Clavien PA, Nocito A. Atraumatic chylous ascites: systematic review on symptoms and causes. J Am Coll Surg 2011; 212: 899–905.

11. Hepburn IS, Seidhar S, Schade RS. Eosinophilic ascites, an unusual presentation of eosinophilic gastroenteritis: a case report and review. World J Gastrointest Pathophysiol 2010; 15: 166–70.

12. Engels M. Cytology of body cavity effusions. J Lab Med 2008; 32: 418–24.

13. Rana SV, Babu SVG. Usefulness of ascitic fluid cholesterol as a marker of malignant ascites. Med Sci Mon 2005; 11: 136–42.

14. Runyon BA. Ascitic fluid bilirubin concentration as a key to choleperitoneum. J Clin Gastroenterol 1987; 9: 543–5.

15. Mansour-Ghanaei F, Safaghi A, Bagherzadeh AH, Fallah MS. Low gradient ascites: a seven year course review. World J Gastroenterol 2005; 11: 2337–9.

47.2 Pleural effusion

The visceral and parietal pleura of the lungs are separated by a potential space of 10–20 μm that contains approximately 0.2 mL of fluid in total per kg of body weight in adults /1/. By its double layer of mesothelial cells, the pleura actively produces substances that maintain the delicate balance between fluid production and reabsorption in the pleural space. The pleural fluid is rich in glycoproteins, has a total protein concentration of approximately 15 g/L, and contains mesothelial cells, macrophages, and lymphocytes. The parietal pleura is supplied by the intercostal arteries and the visceral pleura derives most of its blood supply from the bronchial arteries. The lymphatics of the visceral and parietal pleura are responsible for maintaining pleural fluid homeostasis. In areas of the peripheral parietal pleura and lower mediastinal pleura naturally occurring pores exist. Particulate matter and cells move directly through these pores into the lymphatic channels. Most of the fluid that accumulates in the pleural spaces derives from the lungs through the visceral pleura and is absorbed primarily through the parietal pleura /1/.

The following mechanisms are responsible for the accumulation of pleural fluid /1, 2/:

• Increased trans pleural hydrostatic pressure (e.g., congestive heart failure, portal hypertension)
• Increased capillary permeability (e.g., para pneumonic effusion due to inflammation, infection, malignancy)
• Impaired lymphatic drainage (e.g., malignancy)
• Decreased colloid osmotic pressure (hypoproteinemia)
• Reduced intrapleural pressure (bronchial obstruction, atelectasis)
• Trans diaphragmatic movement of fluid from the peritoneal space to the pleural space (e.g., hepatic hydrothorax)
• Pleural effusion of extravascular origin (e.g., chylothorax or peritoneal dialysis).

47.2.1 Transudate and exudate

One of the first steps in the investigation of patients with pleural fluid is to distinguish those who have exudative (inflammatory) effusions from those with transudative (non inflammatory) effusions /2/.

Transudate

Transudates derive from the ultrafiltration of fluid across the pleural membrane and are low in protein. They result from a non inflammatory process due to increased pulmonary hydrostatic pressure or reduced osmotic pressure of the plasma with no pleural disease involvement /2/. Congestive heart failure is the most common cause of transudative pleural effusions; other less frequent causes include liver cirrhosis and hypoproteinemia.

Exudate

Exudates are formed by active secretion or leakage of the pleural membrane. The pleura is involved by an inflammatory or malignant process causing increased permeability. Exudates have a higher protein content than transudates. A pleural effusion may have a pulmonary, pleural, or extra pulmonary cause.

Exudative pleural effusions occur in the following situations:

• The pleural surface is involved in an inflammatory or infiltrative process that increases capillary permeability
• Drainage of pleural fluid across the parietal pleura is decreased.

The most important etiological factors are inflammatory, infective, neoplastic or are caused by medications (amiodarone, phenytoin, nitrofurantoin and methotrexate) /1/.

If the laboratory is asked to distinguish between a transudate or exudate, it is asked to identify the possible cause of the pleural effusion.

47.2.2 Etiology of pleural effusion

Transudates and exudates can be diagnosed using imaging procedures even in the absence of clinical symptoms (e.g., in intensive care patients with atelectasis or patients with hypoalbuminemia) /1/.

A massive unilateral pleural effusion indicates malignant disease and, in approximately 70% of cases, is an exudate. Bilateral effusions, on the other hand, are mainly transudates that occur in the context of a well established disease process.

Important diagnostic information can be obtained from the history e.g., whether the patient has a history of pneumonia or pleuritis, has undergone coronary artery bypass surgery (especially involving removal of the internal mammary arteries) or radiotherapy, or has worked with asbestos.

When a pleural effusion reaccumulates within 24–72 h following therapeutic thoracentesis, transudative causes such as trapped lung, peritoneal dialysis, hepatic hydrothorax and extravascular migration of a central venous catheter (with saline or glucose solution) should be considered /1/.

Exudates that recur rapidly following thoracocentesis can occur in aggressive vascular tumors such as angiosarcoma or in chylothorax.

Clinical assessment of the patient often provides sufficient information to decide whether thoracocentesis is required. For example, bilateral transudative effusions in the context of an established disease process do not need to be investigated. Unilateral effusions, however, should always be investigated further.

47.2.3 Pleural fluid aspiration

The British Thoracic Society guidelines recommend /3, 4/:

• A diagnostic pleural fluid sample should be collected with a fine bore (21G) needle and a 50 mL syringe
• The sample should be placed in both sterile vials and blood culture bottles
• A heparin tube is preferred for biochemical analyses
• The sample for glucose measurement should be preserved in a fluoride-oxalate tube
• A citrate containing bottle is preferred for cytological investigations
• The sample for pH measurement should be collected anaerobically in a heparinized blood gas syringe to obtain an anaerobic sample
• A sterile container is used for microbiological examinations (Gram stain, acid-fast bacilli, fungi)

47.2.4 Sample appearance

The appearance and odor of the pleural fluid should be noted and all blood stained and milky samples should be centrifuged. The appearance of the sample may be a helpful guide to the etiology /3, 4/:

• An exudate is indicated by a blood-stained, cloudy appearance prior to centrifugation or by a putrid odor
• Following centrifugation, a pleural fluid hematocrit of more than 50% the patient’s serum hematocrit confirms a hemothorax
• Samples that are visibly hemolyzed following centrifugation are not suitable for clinical chemistry analysis.
• If the supernatant from a turbid or milky sample is clear an empyema is likely and if the sample remains turbid a chylothorax is probable. Triglyceride determination should be used to confirm or exclude chylothorax.

47.2.5 Biochemical investigations

One of the first steps in the biochemical investigation of pleural effusions is to distinguish exudative (inflammatory) effusions from transudative (non inflammatory) effusions /2/. Differentiation is made using the protein concentration or Light’s criteria. For Light’s criteria and additional biochemical tests refer to

• Tab. 47.2-1 – Light’s criteria for exudative effusions
• Tab. 47.2-2 – Laboratory tests used to evaluate the etiology of pleural effusions.

47.2.6 Clinical significance of findings

The causes and diseases associated with pleural effusions refer to

• Tab. 47.2-3 – Causes of pleural effusions
• Tab. 47.2-4 – Diseases associated with pleural effusions.

The most useful finding for differentiating a transudate from an exudate is the total protein level of the pleural fluid. A concentration of less than 25 g/L indicates a transudate, whereas a concentration of greater than 35 g/L indicates an exudate. In many samples, however, the total protein concentration is between 25 and 35 g/L and is therefore inconclusive. For this reason, many investigators rely on Light’s criteria /5/. These criteria have a diagnostic sensitivity of 100% for diagnosing an exudate. However, 15–30% of transudates are misclassified based on these criteria so many authors recommend additional investigations, decision trees, or different cutoff values /6/.

Since it is not possible to obtain a sample of normal pleural fluid, reference intervals for biochemical analysis cannot be determined; pleural fluid samples are therefore compared with serum samples obtained at the same time.

During respiration pleural fluid functions as a lubricant that surrounds the lungs allowing the two layers of pleura to glide smoothly past each other. A pH of less than 7.20 determines the need for chest tube drainage because pleural effusions are caused by pneumonia. The pH in pleural fluid is also a predictor of survival inpatients with malignant pleural effusions /17/.

47.2.6.1 Nonmalignant pleural effusions

Nonmalignant pleural effusion is common, with congestive heart failure representing the leading cause. In a study /7/ patients with cardiac, renal, and hepatic failure had 1-year mortality rates of 50%, 46%, and 25%, respectively. Bilateral effusions (hazard ratio 3.55) and transudative effusions (hazard ratio 2.78) were associated with a worse prognosis, with a 57% and 43% 1-year mortality rate, respectively.

47.2.6.2 Malignant pleural effusions

Malignant pleural effusions are the second leading cause of exudative effusions. The majority of exudates arise from lung cancer, breast cancer and lymphoma. Approximately 15% of patients with lung cancer will have malignant pleural effusion at presentation and up to 50% will have malignant pleural effusion during the course of their illness /8/.

A number of factors may help to predict survival of patients with malignant pleural disease, including tumor characteristics, extent of disease, comorbidities and the composition of the effusion. The LENT scoring system is a prognostic score in patients with malignant pleural effusion which may aid clinical decision making in this diverse population. The LENT prognostic score (Pleural fluid lactate dehydrogenase, Eastern Cooperative Oncology Group (ECOG) performance score, neutrophil-to-lymphocyte ratio and tumor type). Patients were typed into low risk, moderate risk and high risk groups with median survivals of 319 days, 130 days and 44 days, respectively /9/.

Refer to Tab. 47.2-5 – The LENT score calculation.

47.2.6.3 Para pneumonic effusions and empyema

Pneumonia associated effusions, so-called parapneumonic effusions are the most common exudative effusions. Empyema refers to frank infection or pus in the pleural space /8/. Pneumonia associated with para pneumonic effusion is associated with higher mortality. Patients with community acquired pneumonia can be infected with Streptococcus species, patients with hospital acquired infection are more likely infected with staphylococus or gram-negative bacteria.

References

1. Jany B, Welte T. Pleural effusions in adults: etiology, diagnosis, and treatment. Dtsch Ärztebl Int 2019; 116: 377–86.

2. Tarn AC, Lapworth R. Biochemical analysis of pleural fluid: what should we measure? Ann Clin Biochem 2001; 38: 311–22.

3. Lapworth R, Tarn AC. Commentary on the British Thoracic Society guidelines for the investigation of unilateral pleural effusions. Ann Clin Biochem 2006; 43: 17–22.

4. Maskell NA, Butland RJA. BTS guidelines for the investigation for a unilateral pleural effusion in adults. Thorax 2003; 58 (Suppl 2): ii8–17.

5. Light RW, McGregor MI, Luchsinger PC, Ball WC. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med 1972; 77: 507–13.

6. Esquerda A, Trujillo J, de Ullibarri IL, Bielsa S, Madronero AB, Porcel JM. Classification tree analysis for the discrimination of pleural exudates and transudates. Clin Chem Lab Med 2007; 45: 82–7.

7. Walker SP, Morley AJ, Stadon L, DE Fonseka D, Arnold DT, Medford ARL, Maskell NA. Nonmalignant pleural effusions: a prospective study of 356 consecutive unselected patients. Chest 2017; 151 (5): 1099–1105.

8. Feller-Kopman D, Light R. Pleural disease. N Engl J Med 2018;378 (8): 740–51.

9. Clive AO, Kahan BC, Hooper CE, Bhatnagar R, Morley AJ, Zahan-Evans N, et al. Predicting survival in malignant pleural effusion: development and validation of the LENT prognostic score. Thorax 2014; 69: 1098–1104.

10. Sahn SA. State of the art. The pleura. Am Rev Respir Dis 1988; 137: 184–234.

11. Sahn SA, Heffner JE. Pleural fluid analysis. In: Light RW, Lee YCG (eds). Textbook of pleural diseases. Hodder A, UK, 2008: 209–26.

12. Brixey AG, Light RW. Pleural effusions occurring with right heart failure. Curr Opin Pulm Med 2011; 17: 226–31.

13. Kennedy C, McCarthy C, Alken S, McWilliams J, Morgan RK, Denton M, et al. Pleuroperitoneal leak complicating peritoneal dialysis: a case series. Int J Nephrology 2011. doi: 10.4061/2011/526753.

14. Hooper CE, Morley AJ, Virgo P, Harvey JE, Kahan B, Maskell NA. A prospective trial evaluating the role of mesothelin in undiagnosed pleural effusions. Eur Resp J 2013; 41: 18–24.

15. Pass HI, Levin SM, Harbut MR, Melamed J, Chiriboga L, Donongton J, et al. Fibulin-3 as a blood effusion marker for pleural mesothelioma. N Engl J Med 2012; 367: 1417–27.

16. Cho Y-Uk, Chi HS, Park CJ, Jang S, Seo EJ, Suh C. Myelomatous pleural effusion: a case series in a single institution and literature review. Korean J Lab Med 2011; 31: 225–30.

17. Zavorsky GS. The stability of pleural fluid pH under slushed ice and room temperature conditions. Clin Chem Lab Med 2022. doi: 10.1515/cclm-2022-0669.

47.3 Pericardial effusion

The pericardial sac is a double walled membrane that surrounds the heart. The outermost layer of the sac is the fibrous pericardium. The fibrous pericardium fuses with the adventitia of the great vessels superiorly, and has ligamentous attachment to the central tendon of the diaphragm inferiorly and the sternum anteriorly. The internal surface of the fibrous pericardium is lined by the parietal layer of the serous pericardium, which is reflected onto the heart as the visceral layer of serous pericardium. The pericardial cavity, therefore, is the space between the parietal and visceral layers /1/. Both layers are separated by a 10–15 mL film of fluid which is an ultra filtrate of plasma (a transudate). The pericardium provides mechanical protection for the heart and the pericardial fluid provides lubrication between the heart and pericardial sac. Approximately 70% of congenital pericardial defects occur on the left heart and 17% occur on the right; the majority of patients with total absence of the pericardium are asymptomatic.

The spectrum of pericardial disease includes congenital defects, pericarditis, neoplasm, and cysts. The etiological classification of pericarditis includes infection, autoimmune disease, post myocardial infarction syndrome, and auto reactive (chronic) pericarditis.

Patients with pericardial effusion and cardiac tamponade may present to any clinical discipline with a variety of symptoms. For slowly developing pericardial effusions, more than 1,000 mL may be required to produce cardiac symptoms of hydrodynamic compression (cardiac tamponade). However, when pericardial fluid accumulates rapidly, as little as 100 mL may greatly relieve cardiac output. Some patients may be asymptomatic while others develop cardiac fibrillation. Cardiac compression generally causes decreased ventricular filling, which in turn leads to a decrease in the stroke volume and cardiac output. If this occurs rapidly, patients present with acute symptoms such as tachycardia, arrhythmia, hypotension, and ECG abnormalities /1/. Most symptomatic non hemorrhagic effusions have a volume of 300–600 mL. Many patients with cardiac tamponade due to a pericardial effusion present with right heart failure affecting the ventricle and atrium /2/.

47.3.1 Etiology of pericardial effusion

Transudates and exudates can be diagnosed using imaging procedures even in the absence of clinical symptoms e.g., in patients with autoimmune pericarditis or those with renal insufficiency and pericardial effusion.

Massive pericardial effusions lead to symptoms of cardiac tamponade, which can be life threatening if it develops rapidly.

The clinical history is of primary importance, e.g. in identifying stab wounds of the heart, a traumatic postsurgical tamponade or evaluating whether the patient has an autoimmune disease or comes from a country with a high prevalence of tuberculosis (Africa, Russia).

The next most important investigation is pericardiocentesis, to determine whether the effusion is a transudate, hemorrhagic effusion, chylous effusion, malignant exudate, or gaseous effusion.

When a pericardial effusion reaccumulates rapidly within 24–72 h of therapeutic pericardiocentesis, causes such as a large anterior wall infarction of the left ventricle or a chylopericardium should be considered.

The causes of pericarditis associated with pericardial effusions are listed in Tab. 47.3-1 – Etiology and incidence of pericarditis.

47.3.2 Differentiation of pericardial effusions

Pericardial effusions occur in association with a wide range of pathological events. Frequently, the etiology is unclear and cannot be determined clinically; this may only be possible at autopsy. Although echo cardiography is an effective, non-invasive method for diagnosing a pericardial effusion, it cannot determine the etiology. However, the presence of an exudate can be confirmed using a limited number of diagnostic methods and, in some cases, a differential diagnosis can be reached based on the history, clinical findings, and specific laboratory determinations.

47.3.3 Sample collection

Samples should be collected as described in Ref. /1/ and transferred to the following tubes for examination:

• Heparin tube for biochemical analysis
• Tube containing sodium fluoride and oxalate for glucose assay
• Citrate containing tube for cytological examination (the specimen should be clot free)
• Sterile container for microbiological examination (Gram staining, acid-fast bacilli, fungi)
• Blood culture bottle for the cultivation of bacteria and fungi.

47.3.4 Sample appearance

The appearance and odor of the sample should be assessed and all turbid samples should be centrifuged:

• A pyogenic effusion is indicated by a blood stained, cloudy appearance prior to centrifugation or by a putrid odor
• Following centrifugation, a pericardial fluid hematocrit that is greater than 50% of the blood hematocrit is diagnostic of a hemopericardium
• Samples that are visibly hemolyzed following centrifugation are not suitable for clinical chemistry analysis
• The presence of a clear supernatant after centrifugation of a turbid or milky sample suggests empyema, whereas a milky supernatant implies a chylous effusion. Triglyceride determination should be used to confirm or exclude a chylous effusion.

Laboratory investigations that are used to differentiate between transudate and exudate and tests that are diagnostically useful in specific situations are outlined in Tab. 47.3-2 – Biochemical investigations in pericardial fluid.

47.3.5 Clinical assessment

Pericardial effusions can occur as a transudate, exudate, pyopericardium, or hemopericardium. Large effusions are common with neoplastic, tuberculous, or uremic pericarditis as well as myxedema, parasitoses, and cholesterol effusions /3/. The most useful finding for differentiating a transudate from an exudate is the total protein concentration. If the total protein is less than 30 g/L, the effusion is a transudate; otherwise, it is an exudate. However, many transudates are misclassified as exudates. Light’s criteria for diagnosing exudative pleural effusions (Tab. 47.3-3 – Light’s criteria for exudative pericardial effusion) were examined for the purpose of diagnosing exudative pericardial effusions and compared with additional criteria in two large studies /4/.

Refer to:

• Tab. 47.3-3 – Light’s criteria for exudative pericardial effusion
• Tab. 47.3-4 – Diagnostic criteria for exudative pericardial effusion
• Tab. 47.3-5 – Diseases associated with pericardial effusion.

References

1. Loukas M, Walters A, Boon JM, Welch TP, Meiring JH, Abrahams PH. Pericardiocentesis: a clinical anatomy review. Clinical Anatomy 2012. doi: 10.1002/ca.22032.

2. Spodick DH. Acute cardiac tamponade. N Engl J Med 2003; 349: 684–90.

3. Maisch B, Seferovic PM, Ristic AD, Erbel R, Rienmüller R, Adler Y, et al. Guidelines on the diagnosis and management of pericardial diseases. Executive summary. Eur Heart J 2004; 25: 587–610.

4. Khandaker MH, Espinosa RE, Nishimura RA, Sinack LJ, Hayes SH, Melduni RM. Pericardial disease: diagnosis and management. Mayo Clin Proc 2010; 85: 572–93.

5. Akyuz S. Arugaslan E, Zengin A, Onuk T, Ceylan US, Yaylak B, et al. Differentiation between transudate and exudate in pericardial effusion has almost no diagnostic value in contemporary medicine. Clin Lab 2015; 61: 957–63.

6. Burgess LJ, Reuter H, Taljaard FJJ, Doubell A. Role of biochemical tests in the diagnosis of large pericardial effusions. Chest 2002; 121: 495–9.

7. Meyers DG, Meyers RE, Prendergast TW. The usefulness of diagnostic tests on pericardial fluid. Chest 1997; 111: 1213–21.

8. Karatolios K, Maisch B, Pankuweit S. Tumormarker im Perikarderguss bei malignen und nichtmalignen Perikardergüssen. Herz 2011; 36: 290–5.

9. Megged O, Argaman Z, Kleid D. Purulent pericarditis in children. Is pericardiotomy needed? Pediatr Emergency Care 2011; 27: 1185–7.

10. Sekhri V, Sanal S, DeLorenzo JL, Aronow WS, Maguire GP. Cardiac sarcoidosis: a comprehensive review. Arch Med Sci 2011; 7: 546–54.

11. Dainese L, Cappai A, Biglioli P. Recurrent pericardial effusion after cardiac surgery: the use of colchicine after recalcitrant conventional therapy. JCTS 2011; 6: 96.

12. Refaat MM, Katz WE. Neoplastic pericardial effusion. Clin Cardiol 2011; 34: 593–8.

13. Posner MR, Cohen GI, Skarin AT. Pericardial disease in patients with cancer: the differentiation of malignant from idiopathic and radiation-induced pericarditis. Am J Med 1981; 71: 407–13.

14. Wagner PL, McAleer E, Stillwell E, Bott M, Rusch VW, Schaffer W, Huang J. Pericardial effusions in the cancer population: prognostic factors after pericardial window and the impact of paradoxical hemodynamic instability. J Thorac Cardiovasc Surg 2011; 141: 34–8.

47.4 Bile and bile acids

Bile ducts

About 5% of cells in the liver are cholangiocytes. These ciliated epithelial cells line the bile tree, an intrinsic network of interconnecting bile ducts that increase in diameter from the ducts of Hering to the extrahepatic bile ducts /1/. Cholangiocytes that line the large interlobular and major bile ducts are predominantly involved in secretion, whereas cholangiocytes that line the cholangioles have roles in inflammatory and proliferative responses. The cilia that extend from the apical cell membrane into the ductal lumen regulate mechanosensory, osmosensory, and chemosensory functions. Cilia detect and signal changes in bile flow and osmolality /2/.

Cholangiocyte stimulation through pro secretory stimuli (triggered by secretin, vasoactive intestinal polypeptide, glucagon, acetylcholine, and bombesin) leads to secretion of water, bicarbonate, and chloride into the bile ducts and to biliary alkalinization. Anti- secretory mechanisms are activated by endothelin 1 and somatostatin. Nuclear receptors in the cholangiocytes (farnesoid X receptor, pregnane X receptor, vitamin D receptor, and constitutive androstane receptor) regulate transcription of genes that encode apical (canalicular) and basolateral (sinusoidal) transport proteins of the cholangiocyte membrane. These transport proteins move bile acids from sinusoidal blood into the bile canaliculi. Active export of bile acids into the bile is mediated by the bile salt canalicular export pump (ABCB11) and the canalicular conjugate export pump (MRP2), which, in addition to bile acids, also exports other organic anions such as bilirubin into the bile duct lumen. Formation of mixed micelles in bile results from the presence of bile acids, cholesterol, and phosphatidylcholine, and the phospholipid export pump multi drug-resistant 3 protein (MDR3), is actively involved in the controlling process /3/.

47.4.1 Composition of the bile

Components of the bile and the reference intervals are shown in Tab. 47.4-1 – Reference intervals for bile analytes. The most important components are bile acids and cholesterol.

Bile acids

Bile acids are amphiphatic with a hydrophobic convex and a hydrophilic concave structure, allowing them to form micelles with water-insoluble cholesterol, nutritional lipids, and fat soluble vitamins /4/. The primary bile acids cholic acid, chenodesoxycholic acid are synthesized from cholesterol in a multi-step pathway in the hepatocytes of the liver. Bile acids are conjugated with glycine or taurine which renders them ionised (bile salts) and are secreted across the canalicular membrane into the biliary tree, from where they drain into the gall bladder. In response to food intake, bile acids stored in the gall bladder are released into the duodenum where they perform their emulsifying function. More than 95% are actively recycled by enterohepatic circulation (taken up by the ileum, passing the portal vein to the liver, and again excreted) /4/. For bile acid biochemistry and metabolism, see Ref. /5,  6/.

Depending on the gut microbiota composition a portion of bile acids are metabolized yielding the major secondary bile acids that are passively reabsorbed in the intestine and returned to the liver or excreted with faeces.

The gut microbiota metabolize primary bile acids and form secondary bile acids:

• by first removing the aminoacid residues (deconjugation)
• then removing 7α-hydroxyl groups from cholic acid and chenodeoxycholic acid yielding deoxycholic acid and lithocholic acid.

Bile acids bind to the G-protein coupled nuclear farnesoid X receptor and are regulators of insulin sensitivity, energy homeostasis, and of their own.

Due to their toxicity, the concentration of bile acids in the plasma and liver is maintained within narrow limits. High concentrations of bile acids in the biliary tree are incompatible with life so phosphatidylcholine is secreted simultaneously to form mixed micelles with the bile acids, thus reducing their detergent activity.

The following three canalicular transporters play an important role in the hepatic secretion of bile and in the etiology of cholestasis /4/:

• The bile acid export pump ABCB11 and the phosphatidylcholine transporter floppase (ABCB4), both of which are members of the ATP-binding cassette (ABC) transporter super family
• The P-type ATPase ATP8B1, which transports phosphatidylserine in the opposite direction to the direction in which phosphatidylcholine is transported by ABCB4.

Bile cholesterol

The liver plays a crucial role in cholesterol metabolism. In addition to expressing lipoprotein receptors for the uptake of cholesterol containing lipoproteins, it also synthesizes cholesterol.

Cholesterol is released from the hepatic pool in two ways /7/:

• Triglyceride-rich VLDL supplies peripheral cells with fatty acids, fat soluble vitamins, and cholesterol
• Secretion of free cholesterol directly into the bile by the ATP binding cassette (ABC) cholesterol transporter ABCG5/G8
• Secretion of bile acids formed from cholesterol into the biliary ducts. A proportion of these bile acids (and therefore, of the cholesterol pool) is lost in the feces.

Biliary cholesterol excretion has a role in the development of two major disease complexes: atherosclerotic cardiovascular disease and gallstones.

Bile micelles

The proportion of bile acids is up approximately 50% of the organic constituents of the bile dry weight. The other major constituent of bile (25%) is phosphatidylcholine. The remainder is a complex mixture of cholesterol, bilirubin, glutathione, pigments, plant sterols, and electrolytes.

Mixed micelles are formed from bile acids, cholesterol, and phosphatidylcholine under the control of the phospholipid export pump MDR3 (multidrug resistance protein 3), which is located in the canalicular hepatocyte membrane. MDR3 deficiency causes progressive familial intrahepatic cholestasis type 3.

47.4.2 Bile secretion

Bile is usually secreted continuously by the liver and, during fasting, around 75% is diverted into the gallbladder where it is concentrated. In response to food intake, the gallbladder contracts and releases the concentrated bile into the duodenum. More than 95% of the bile acids in the intestine are reabsorbed and transported back to the liver.

Hepatic bile formation occurs at two levels, canalicular and ductular. Canalicular bile flow is mainly dependent on bile acid secretion and accounts for 70–85% of the total canalicular flow. Bile acid independent bile flow is driven by inorganic ion transport and is both canalicular and ductular /8/.

Although bile is sterile under normal conditions, bacterial components such as lipopolysaccharides (LPS), lipoteichoic acid, and bacterial DNA fragments [collectively known as pathogen associated molecular patterns (PAMPs)] are detectable. The presence of PAMPs indicates that biliary epithelial cells are exposed to bacteria under physiological and pathological conditions /9/.

47.4.3 Bile collection

There are different types of bile.

Native bile

Approximately 0.5–1 L of native bile (also known as bile duct bile or “A” bile) is produced continuously. Native bile is yellow and is diverted into the gallbladder where it is concentrated by the withdrawal of water.

Gallbladder bile

Gallbladder bile (also known as “B” bile) is concentrated bile that is expelled into the duodenum postprandially. It has a volume of approximately 100 mL and is composed of: water (82%); bile acids (12%); phospholipids (4%); cholesterol (0.7%); bile pigments, proteins, and electrolytes (less than 1%). It has a pH of 5.6–8.0.

White bile

White bile is a colorless, translucent fluid of low viscosity that is found following biliary obstruction.

Bile collection

Native bile: this type of bile can be collected during endoscopic retrograde cholangiography. It can also be collected following cholecystectomy using a T-tube.

Gallbladder bile: gallbladder puncture.

Bile-containing duodenal juice: a Dreiling gastroduodenal tube is used to avoid contamination with gastric juice.

47.4.4 Clinical significance of bile

The bile acids are the most important component of bile and the only component with digestive activity (apart from the phospholipids, which have lipid emulsifying effects). Bile acids promote the intestinal effects of pancreatic enzymes and enhance the secretin-pancreoyzmin-cholecystokinin stimulation of pancreatic juice during meals. A reduction in the quantity of bile acids in the intestine leads to chologenic digestive disturbance.

Intrahepatic and extrahepatic cholestasis disrupt bile flow, which leads to digestive dysfunction and an increase in the plasma bile acid concentration. The main clinical effect is pruritus due to elevated concentrations of bile acids in the skin. In primary biliary cirrhosis, for example, pruritus may occur years before other symptoms.

In liver cirrhosis, bile acid synthesis is reduced by up to 50%, which explains the steatorrhea experienced by some of these patients.

Chologenic digestive disturbances can also occur in patients with bile acid malabsorption or following ileal resection, due to disruption of the normal enterohepatic circulation of bile acids; the liver is unable to compensate for a reduction of more than 20% in this enterohepatic circulation.

The main symptom experienced by patients with bile acid malabsorption is diarrhea, caused by osmotically active bile acids flooding the colon. Steatorrhea is a prominent symptom in severe cases.

In addition to quantitative decreases in bile acids, qualitative changes also play a role /10/. For example, a blind pouch can form as the result of a side-to-side anastomosis of the intestine, or chyme can stagnate in the intestine as a result of diverticula or stenosis (stagnant loop syndrome). Local bacteria and bacteria from the oropharynx can then deconjugate the bile acids. The resulting free bile acids are poorly water-soluble and leak from the intestinal lumen into the blood by passive reabsorption in the jejunum. All of this leads to digestive disturbances.

Tab. 47.4-2 – Diseases associated with changes in bile composition lists diseases that are associated with altered bile composition.

47.4.5 Bile acids in serum

Indication

The diagnosis of bile acid malabsorption is an important indication for the determination of bile acids in serum.

Method of determination

Total bile acids are determined according to the enzymatic fluorimetric method, the luminometric method or using gas-liquid chromatography /11/.

Specimen

Serum: 1 mL

Reference interval /11/

• Total bile acids (x ± s)
• Fasting individuals: < 9 μmol/L (4.3 ± 2.3 μmol/L)
• Non-fasting individuals: 1–12 μmol/L (6.2 ± 2.8 μmol/L)

Clinical significance

The serum concentration of total bile acids in hepatobiliary disease is increased (Tab. 47.4-3 – Concentration of total serum bile acids in liver disease). Changes in serum bile acids are seen in quite mild liver disturbances. Serum bile acids normally increase 2–4-fold after eating, with a postprandial peak at 60–90 minutes. Normal fasting serum total bile acids being less than 6.4 μmol/L. A 2 hour post-prandial bile acid concentration > 20 μmol/L is suggestive of a hepatobiliary disease.

The bile acid levels are decreased in bile acid malabsorption (BAM). Three types are differentiated:

• Type 1; BAM results from disease of the ileum, resection of the ileum or ileum bypass
• Type 2; primary or idiopathic BAM
• Type 3; BAM resulting from cholecystectomy, vagotomy or associated with other disease.

The common causes of bile acid malabsorption are ileal resection and diseases of the terminal ileum (Crohn’s disease and radiation enteritis), which result in a loss of bile acid transporters and consequently, diminishes reabsorption. Bile acid malabsorption also occurs in a small group of patients with watery diarrhea who have no ileal disease (idiopathic bile acid malabsorption). The amount of bile acid loss to the colon determines the clinical presentation /12, 13/.

Congenital bile acid synthesis defect type 1 is a disorder characterized by cholestasis. Individuals with this defect cannot produce bile acids /14/. The signs and symptoms develop in the first week of life, but they can begin any time from infancy to childhood. Affected infants have a failure to thrive, jaundice and excess fat in the feces. The prevalence of the defect is thought to be 1 to 9 per million people. Mutations in the HSD3B7 gene cause the synthesis defect. The gene codes the enzyme 3 β-hydroxysteroid dehydrogenase type 7 which is responsible for the conversion of 7α-hydroxy cholesterol to 7α-hydroxy-4-cholesten-3-one /15/.

The composition of gall stones is shown in Tab. 47.4-4 – Gall stone composition.

References

1. Hirschfield GM, Heathcote J, Gershwin ME. Pathogenesis of cholestatic liver disease and therapeutic approaches. Gastroenterology 2010; 139: 1481–96.

2. Masyuk AI, Gradilone SA, Banales JM, et al. Cholangiocyte cilia are chemosensory organelles that detect biliary nucleotides via P2Y12 purinergic receptors. Am J Physiol Gastrointest Liver Physiol 2008; 295: G725–G734.

3. Davit-Spraul A, Gonzales E, Baussan C, et al. The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects. Semin Liver Dis 2010; 30: 134–46.

4. Nicolaou M, Andress EJ, Zolnerciks JK, Dixon PH, Williamson C. Canalicular ABC transporters and liver disease. J Pathology 2012; 226: 300–15.

5. Markus C, Coat S, Marschall HU, Williamson C, Dixon P, et al The BACH project protocol: an international multicentre total bile acid comparison and harmonisation project and sub-study of the turrific randomized trial. Clin Chem Lab Med 2021;59 (12): 1921–9.

6. Chiang JYL. Bile acids: regulation and synthesis. J Lipid Res 2009; 50: 1955–66.

7. Dikkers A, Tietge UJF. Biliary cholesterol secretion: more than a simple ABC. World J Gastroenterol 2010; 21: 5936–45.

8. Tsonuda T, Eto T, Furukawa M, Nakata T, Kusano T, Lin Y, et al. Clear and colorless fluid observed during percutaneous transhepatic gallbladder drainage: Gastroenterology Jpn 1990; 25: 619–24.

9. Heil W, Edelmann J, Kiemstedt W, Zawta B. Reference ranges for analytes in extravascular body fluids. Clin Lab 2001; 47: 7–16.

10. Begemann F. Die Bedeutung der Gallensäuren für die Verdauung. Med Klin 1973; 68: 1024–9.

11. Bergmeyer HU. Methods of enzymatic analysis, Vol VIII, p. 267–315. VCH, Weinheim, 1981.

12. Westergaard H. Bile acid malabsorption. Curr Treat Options Gastroenterol 2007; 10: 28–33.

13. Pattni S, Walters JRF. Recent advances in the understanding of bile acid malabsorption. Br Med Bulletin 2009; 92: 79–93.

14. Sundaram SS, Bove KE, Lovell MA, Sokol RJ. Mechanisms of disease. Nature Clin Pract Gastroenterol Hepatol 2008; 5: 456–68.

15. de Aguiar Vallim TQ, Tarling EJ, Edwards PA. Pleiotropic roles of bile acids in metabolism. Cell Metabolism 2013; 17: 657–69.

16. Skrede S, Solberg HE, Blomhoff JP, Gjone E. Bile acids measured in serum during fasting as a test for liver disease. Clin Chem 1978; 24: 1095–9.

17. Gravante G, Knowles T, Ong SL, Al-Taan O, Metcalf M, Dennison AR, Lloyd DM. Bile changes after liver surgery: experimental and clinical lessons for future applications. Dig Surg 2010; 27: 450–60.

18. Bajor A, Gillberg PG, Abrahamsson H. Bile acids: short and long term effects in the intestine. Scand J Gastroenterol 2010; 45: 645–64.

19. Wittenburg H. Hereditary liver disease: gallstones. Best Practice & Research Clinical Gastroenterology 2010; 24: 747–56.

20. Smelt AH. Triglycerides and gallstone formation. Clin Chim Acta 2010; 411: 1625–31.

21. Akiyoshi T, Nakayama F. Bile acid composition in brown pigment stones. Dig Dis Sci 1990; 35: 27–32.

47.5 Amniotic fluid

Amniotic fluid from a physicochemical view is a heterogeneous system composed of a solution in which undissolved material (cells and organized matter) are suspended. Following centrifugation, it is almost as clear as water; however, its specific gravity and osmolality are significantly higher. Amniotic fluid consists of around 98% water and 2% solids. The inorganic constituents resemble interstitial fluid i.e., the concentration of Na⁺, Cl^– and CO₂ are high with only small amounts of K⁺, Ca²⁺, Mg²⁺ and phosphate /1/. About one-half of the solids are organic and about one-half of the organic solids are proteins.

Amniotic fluid volume

The precise volume of amniotic fluid depends on the week of gestation but the mean volume is 800–1,000 mL /2/. An amniotic fluid volume of greater than 2,200 mL in the 34th week of gestation is referred to as polyhydramnios while a volume of less than 318 mL is referred to as oligohydramnios. Fetal urine enters the amniotic fluid each day: on average 70 mL/day in the 20th gestational week, 229 mL/day in the 30th gestational week, and 796 mL/day in the 40th gestational week. In addition, starting in gestational week 10–20, an average of 100 mL/kg body weight of fetal lung secretions is added to the amniotic fluid each day. The fetus swallows 4–11 mL of amniotic fluid each day from the 18th gestational week, increasing to 210–760 mL shortly before delivery.

47.5.1 Amniotic fluid analysis

Sample appearance

Amniotic fluid is usually clear and slightly yellow or white. Greenish discoloration or meconium staining may indicate fetal hypoxia. Greenish-brownish discoloration may indicate the presence of hemoglobin degradation products. Blood stained amniotic fluid, which may be discharged from the vagina, should be examined for the presence of fetal erythrocytes. The reference intervals for the analytes in amniotic fluid are listed in Tab. 47.5-1 – Amniotic fluid reference intervals.

47.5.1.1 Differentiation of amniotic fluid from urine

It is important to distinguish amniotic fluid from urine in cases of suspected amniotic fluid leakage. The determination of creatinine, urea, and K⁺ are used for differentiation /4/.

Refer to Tab. 47.5-2 – Differentiation between amniotic fluid and urine).

47.5.1.2 Meconium-stained amniotic fluid

Meconium stained amniotic fluid does not indicate neonatal hypoglycemia. In one study /3/ of 803 infants born following observation of meconium stained amniotic fluid, 8.5% had blood glucose levels below 47 mg/dL (2.6 mmol/L) but only 0.4% had severe hypoglycemia.

47.5.1.3 Polymerase chain reaction (PCR) in amniotic fluid

Ultrasound examination plays a vital role in the prenatal identification and diagnosis of fetal structural anomalies and anatomical abnormalities. If abnormalities are detected on ultrasound, chromosomal investigations using chorionic villus sampling or amniocentesis have an important role in clarifying the diagnosis. It is also possible that PCR should be performed as part of these investigations in order to test for viral infections. In a study /5/ of 1,191 amniotic fluid samples, an abnormal karyotype was detected in 5.4% and PCR testing for viruses was positive in 6.5%. Intrauterine growth restriction, non immune hydrops fetalis, hand/foot anomalies, and neural tube defects were associated with positive PCR for viruses. The most frequently isolated viral genomes were Adenovirus and Cytomegalovirus. Amniotic fluid viral PCR testing should be considered for fetuses with intrauterine growth retardation, non immune hydrops fetalis, hand/foot anomalies, or neural tube defects.

Simple and accurate diagnosis of vertical transmission of Toxoplasma gondii and Parvovirus B19 in amniotic fluid remains an important issue in pregnancy.

Toxoplasmosis

In women with T. gondii infection acquired during pregnancy the risk of fetal infection was 7.4%. The PCR test in amniotic fluid performed better than conventional parasitologic methods (diagnostic sensitivity, 97.4% vs. 89.5%; negative predictive value, 99.7% vs 98.7%) /6/.

Human Parvovirus B19 infection (B19V)

In a study /7/ the B19V DNA concentrations in maternal sera and amniotic fluid ranged from 10⁴ to 10⁵ copies/mL and 10⁷ to 10⁸ copies/mL, respectively. All pregnant women contracted the B19V infection between 13 to 14 weeks gestation and were investigated between 16 to 27 weeks of gestation. Amniotic fluids may indicate fetal B19V infection at an early stage of pregnancy and may substitute fetal sera.

References

1. Bonsnes RW. Composition of amniotic fluid. Clin Obstet Gynecol 1966; 9: 440–8.

2. Ross MG, Brace RA and the NIH Workshop Participants. National Institute of Child Health and Development conference summary: amniotic fluid biology – basic and clinical aspects. J Maternal-Fetal Med 2001; 10: 2–19.

3. Maayan-Metzger A, Leibovitch L, Schushan-Eisen I, Strauss T, Kuint J. Meconium-stained amniotic fluid and hypoglycemia among term newborn infants. Fetal Pediatr Pathol 2012; published ahead.

4. Campbell J, Wathen N, MacIntosh M, Cass P, Chard T, Mainwaring-Burton R. Biochemical composition of amniotic fluid and extraembryonic coelomic fluid in the first trimester of pregnancy. Br J Obstet Gynecol 1992; 99: 563–5.

5. Adams LL, Gungor S, Turan S, Kopelman JN, Harman CR, Baschat AA. When are amniotic fluid viral PCR studies indicated in prenatal diagnosis? Prenatal Diagnosis 2012; 32: 88–93.

6. Hohlfeld P, Daffos P, Costa JM, Thulliez P, Forestier F, Vidaud M. Prenatal diagnosis of congenital toxoplasmosis with a polymerase-chain reaction test on amniotic fluid. N Engl J Med 1994; 331: 695–9.

7. Ishikawa A, Yoto Y, Asakura H, Tsutsumi H. Quantitative analysis of human parvovirus B19 DNA in maternal and fetal serum, and amniotic fluid during an early stage of pregnancy. J Med Virol 2015; 87: 683–5.

47.6 Lymph

Lymph is a clear, usually slightly yellow fluid that absorbs the capillary filtrate from the tissues and transports it through the lymphatic system to the thoracic duct, from where it drains into the left subclavian vein. See Section 47.2 – Pleural effusion. Lymph that drains from the stomach and intestine after eating is turbid or chylous and, because it contains chylomicrons, is referred to as chyle.

Non-chylous lymph drains from other areas, such as the lungs. In total, approximately 1.5–2.5 L of lymph drains into the venous system each day; around 1 L of this originates in the thorax.

The reference intervals for the main biochemical analytes in lymph are shown in Tab. 47.6-1 – Lymph reference intervals.

For chylous pleural effusions, see Section 47.2 – Pleural effusion.

For chylopericardium, see Tab. 47.3-5 – Diseases associated with pericardial effusion and Ref. /2/.

References

1. Valentine VG, Raffin TA. The management of chylothorax. Chest 1992; 102: 586–91.

2. Maisch B, Seferovic PM, Ristic AD, Erbel R, Rienmüller R, Adler Y, et al. Guidelines on the diagnosis and management of pericardial diseases. Executive summary. Eur Heart J 2004; 25: 587–610.

47.7 Gastric juice

The gastric juice consists of an acid secretion produced by the parietal cells mixed with an alkaline secretion produced by other gastric mucosal cells. It is secreted in response to neural and humoral stimuli.

Gastric acid secretion is regulated by the following feedback loop:

• H⁺ is secreted in response to stimulation by the vagus nerve and the hormones gastrin and histamine
• If acidic gastric contents spill into the duodenum, H⁺ secretion is inhibited by the hormones secretin, vasoactive intestinal polypeptide, and gastric inhibitory polypeptide.

There is a direct correlation between the parietal cell mass and the capacity of the stomach to secrete H⁺. Pepsinogens are produced by the chief cells and gastrin is produced by the G cells of the pyloric antrum. Approximately 1–3 liters of gastric fluid are secreted every 24 hours.

Analysis of gastric acid secretion following maximal stimulation with pentagastrin provides information about the functional status of the gastric mucosa (maximal acid output, MAO). In this test, first the basal secretion and then the secretion following pentagastrin stimulation are each measured for an hour by continuous aspiration through a gastric tube. In healthy individuals, basal H⁺ secretion (basal acid output, BAO) is less than 5 mmol per hour and stimulated secretion is 20–25 mmol per hour. Significantly elevated basal secretion levels are observed in Zollinger-Ellison syndrome. In this condition, the BAO/MAO ratio is greater than 0.6.

The reference intervals for the analytes in gastric juice are shown in Tab. 47.7-1 – Gastric juice reference intervals.

In Helicobacter pylori gastritis, the ammonium level in the gastric juice can be elevated 5–10-fold.

In suspected pulmonary tuberculosis, a specimen of aspirated gastric juice can be used to cultivate Mycobacterium tuberculosis with a diagnostic sensitivity of 89% /3/.

References

1. Heil W, Edelmann J, Kiemstedt W, Zawta B. Reference ranges for analytes in extravascular body fluids. Clin Lab 2001; 47: 7–16.

2. Lindahl A, Ungell AL, Knutson L, Lenneräs H. Characterization of fluids from the stomach and proximal jejunum in men and women. Pharm Res 1997; 14: 497–502.

3. Rüsch-Gerdes S. Mykobakterien Kultursysteme. Lab Med 1991; 15: 232–3.

47.8 Nasal secretion

47.8.1 Increased nasal secretion

The nasal mucosa is regularly exposed to viral and bacterial infections. A wide range of pathogens gain access to the body via the nasal mucosa, including viruses responsible for the common cold, Influenza virus, Measle virus, and Mumps virus, as well as Bordetella pertussis. The activation of inflammatory mediators leads to vasodilation and increased capillary permeability, which results in plasma exudation and increased nasal secretion. The main components of nasal secretion are produced by filtration though the highly permeable fenestrated capillaries of the nasal mucosa /1/.

Nasal polyps are another cause of increased nasal secretion. Polyps develop from edematous tissue that is infiltrated by neutrophils, eosinophils and plasma cells. The nasal secretion of patients with nasal polyps contains higher concentrations of protein, albumin, secretory IgA, IgG, and (in IgE-mediated allergy) IgE than the nasal secretion of controls /2/.

47.8.2 Cerebrospinal fluid leakage

The CSF leakage may occur as post-traumatic, iatrogenic, spontaneous or idiopathic rhinorrhea. Cerebrospinal rhinorrhea results from fistula formation between the dura matter and the skull base. The most common sites are the ethmoid and frontal sinuses. CSF can leak from the nose as CSF rhinorrhea or across the temporal bone and middle ear into the auditory canal as CSF otorrhea.

Sample collection

In CSF rhinorrhea, fluid is collected by inserting a pad into the nasal cavity and in CSF otorrhea, by puncturing the middle ear.

Differentiation of nasal secretion from CSF

The most important determinations used to differentiate between nasal secretion and CSF are β-trace protein, the main protein in the CSF, and β₂-transferrin. Differences between the concentrations of various analytes in nasal secretion and CSF are shown in Tab. 47.8-1 – Reference intervals for analytes in nasal secretion and CSF.

Biomarkers such as β₂-transferrin and β-trace protein are necessary to identify cerebrospinal fluid leakage /3/.

References

1. Persson CGA, Erjefalt I, Alkner U, Baumgarten C, Greiff L, Gustafsson B, et al. Plasma exudation as a first line respiratory mucosal defence. Clin Exp Allergy 1991; 21: 17–24.

2. Biewenga J, Stoop AE, van der Heijden HAMD, van der Baan S, van Kamp GJ. Albumin and immunoglobulin levels in nasal secretions of patients with nasal polyps treated with endoscopic sinus surgery and topical corticosteroids. J Allergy Clin Immunol 1995; 96: 334–40.

3. Mantur M, Lukaszewicz-Zajac M, Mroczko B, Kulakowska A, Ganslandt O, Kemona H, et al. Cerebrospinal fluid leakage – reliable diagnostic methods. Clin Chim Acta 2011; 412: 837–40.

4. Arrer E, Meco C, Oberascher G, Piotrowski W, Albegger K, Parsch W. β-trace protein as a marker for cerebrospinal fluid rhinorrhoea. Clin Chem 2002; 48: 939–41.

5. Bachmann G, Achtelik R, Nekic M, Michel O. Beta trace Protein in der Diagnostik der Liquorfistel. HNO 2000; 48: 496–500.

6. Delaroche O, Bordure P, Lippert E, Sagniez M. Perilymph detection by β₂-transferrin immunoblotting assay. Application to the diagnostic of perilymphatic fistulae. Clin Chim Acta 1996; 245: 93–104.

7. Heil W, Edelmann J, Kiemstedt W, Zawta B. Reference ranges for analytes in extravascular body fluids. Clin Lab 2001; 47: 7–16.

47.9 Tear fluid

The lacrimal glands secrete a liquid film that protects the cornea from drying out. Determinations that are used to characterize the tear fluid are listed in Tab. 47.9-1 – Analytes in tear fluid.

References

1. Heil W, Edelmann J, Kiemstedt W, Zawta B. Reference ranges for analytes in extravascular body fluids. Clin Lab 2001; 47: 7–16.

2. Meillet D, Hoang PL, Unanue F, Kapel N, Diemert MC, Rousellie F, et al. Filtration and local synthesis of lacrimal proteins in acquired immunodeficiency syndrome. Eur J Clin Chem Clin Biochem 1992; 30: 319–23.

47.10 Sweat

Sweat (perspiration) is a dilute electrolyte solution that contains low concentrations of other components. One of its main functions is to regulate the body temperature. There are two main types of sweat:

• Exocrine sweat, which is produced by exocrine cells on the skin surface and secreted in response to cholinergic sympathetic stimulation. Exocrine sweat glands consist of a secretory coil and an excretory duct.
• Apocrine sweat. This type of sweat is secreted by apocrine cells in the hair follicles of the axillary and pubic regions. Its secretion is stimulated mainly by epinephrine.

An adult who has lived for 1–6 weeks in a hot climate produces approximately 700 mL of sweat per hour under hot conditions without air conditioning. This can increase to 1,500 mL per hour during prolonged physical activity in the heat. The concentration of electrolytes, glucose, urea, and protein in thermally induced sweat increases with age and, with the exception of protein, is higher in males than in females /1/. The reference intervals for analytes of sweat /1, 2/ are shown in Tab. 47.10-1 – Reference intervals for analytes in sweat.

47.10.1 Cystic fibrosis

Cystic fibrosis is one of the most common hereditary diseases, with an incidence of 1 : 3200 in Caucasians and 1 : 15,000 in Africans and Asians. Disorder of mucosal absorption of the lung surface and glandular epithelium of the airways is the main contributor to morbidity. Tenacious secretions obstruct the distal airways of the lung and submucosal glands. Ductular dilatation of these glands and the plastering of airway surfaces by thick, viscous, neutrophil granulocyte dominated mucopurulent debris are pathological hallmarks of cystic fibrosis. The mucopurulent debris is an excellent nutriment medium for pathogens (e.g., H. influenzae, S. aureus, Pseudomonas sp., Burkholderia sp.). There is agreement that defects in ion transport and salt homeostasis are linked to organ damage in cystic fibrosis /3/.

The apical plasma membrane of cells of the of the lung surface and glandular epithelium of the airways contains the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR is part of a multi protein assembly that conducts Cl^– across the cell membrane /3/. More than 1500 mutations leading to functional impairment of the CFTR have been identified to date. In bronchial mucosal cells, for example, reduced secretion of Cl^– leads to increased influx of Na+ and water into the cell. Water is withdrawn from the bronchial secretions, increasing their viscosity.

Sweat glands have pronounced abnormalities in comparison to epithelial cells of the lung surface and glandular epithelium of the airways /3/. Under normal conditions, Na+ following Cl^– counter ion is avidly reabsorbed from the ductular lumen, primarily through apical Na+ channels and CFTR. In cystic fibrosis, the absence of functioning CFTR restricts reabsorption of Cl^–, thereby limiting the amount of salt that can be reclaimed. Because there is no other pathway for Cl^– reabsorption in the duct, Na⁺ is also poorly absorbed, and sweat emerging on the skin surface contains a high level of salt /3/.

The pilocarpine iontophoresis sweat test is used to diagnose cystic fibrosis.

47.10.1.1 Standardized sweat test

Principle /4/: transdermal administration of pilocarpine by iontophoresis to stimulate sweat gland secretion, followed by collection and quantization of sweat onto gauze or filter paper or into a macro duct coil and analysis of Cl^– concentration.

Test interpretation: according to the US Cystic Fibrosis Foundation Consensus Report /4/ using the original standardized sweat test universal definitions are:

• Cl^– concentration ≤ 39 mmol/L; normal
• Cl^– concentration 40–59 mmol/L; intermediate
• Cl^– concentration ≥ 60 mmol/L; abnormal.

In the 2005 US Cystic Fibrosis Foundation Patient Registry, only 3.5% of patients with a diagnosis of cystic fibrosis had a sweat Cl^– concentration < 60 mmol/L, and only 1.2% had a value < 40 mmol/L /4/.

Cystic fibrosis is an autosomal recessive disease caused by variants in the CFTR gene /5/.

References

1. Al-Tamer YY, Hadi EA. Age dependent reference intervals of glucose, urea, protein, lactate and electrolytes in thermally induced sweat. Eur J Clin Chem Clin Biochem 1994; 32: 71–7.

2. Heinemann ML, Hentschel J, Becker S, Prenzel F, Henn C, Kiess W, et al. Einführung des deutschlandweiten Neugeborenenscreenings für Mukoviszidose. J Lab Med 2016;40 (6): 373–84.

3. Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med 2005; 352: 1992–2001.

4. Farrell PM, Rosenstein BJ, White TB, Accurso FJ, Castellani C, Cuttig GR, et al. Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation Consensus Report. J Pediatr 2008; 153: S4–S14.

5. Grasemann H. Cystic fibrosis. N Engl J Med 2023; 389 (18): 1693–1707.

47.11 Urine

The composition of morning urine of apparently healthy probands adequately reflects excretion of 24 hours /1/. Refer to Tab. 47.11-1 – Comparison of 24 h urine and the first morning urine of apparently healthy persons.

References

1. Krieg M, Gunßer KJ, Steinhagen-Thießen E, Becker H. Vergleichende quantitative Analytik klinisch-chemischer Kenngrößen im 24-Stunden-Urin und Morgenurin. J Clin Chem Clin Biochem 1986; 24: 863–9.

47.12 Pancreatic cyst fluid

Pancreatic cysts are often detected incidentally on routine abdominal ultrasound and comprise a clinically challenging situation. The reason for pancreatic cystic leasons can be /1/:

• Non-neoplastic cysts
• Cystic neoplasms
• Solid neoplasms containing cysts.

Retention cysts, pseudocysts and serous cystadenoma are benign pancreatic cysts. However, there is a risk of malignancy in some pancreatic cysts it is important to determine the type of cyst lesion. After fine needle aspiration tests like determination of cyst fluid cytology, viscosity, glucose, CEA, CA19-9 are applied in clinical practice. In a study /2/ the diagnostic performance of cyst fluid CEA, glucose and a combination of both differentiating mucinous from non-mucinous neoplastic pancreatic cystic lesions was determined. The ideal cut-offs are shown in Tab. 47.12-1 – Test performances to rule-in and to rule-out mucinous neoplastic pancreatic cyst fluid.

References

1. Lee LS. Diagnostic approach to pancreatic cysts. Curr Opin Gastroenterol 2014; 30 (5): 511–7.

2. Barutcuoglu B, Oruc N, Günes Ak, Kucukokudan S, Aydin A, Nart D, et al. Co-analysis of pancreatic cyst fluid carcinoembryonic antigen and glucose with novel cut-off levels better distinguishes between mucinous and non-mucinous neoplastic pancreatic cyst lesions. Ann Clin Biochem 2022; 59 (2): 125–33.

47.13 Third space fluid loss

The third space is a fluid compartiment, that typically has little or no fluid (e.g., ascites, pleural effusion). Accumulation of fluids develop pathologically in these spaces. Fluids in such spaces are mostly transudates which are protein-poor. When pathogenic events alter the equilibrium

• between oncotic and hydrostatic pressure
• between capillary membrane permeability and lymphatic capacity

third space fluid will develop. This is the case in patients with heart failure with preserved ejection fraction, leading to the development of a pleural transudate.

In patients with inflammatory disorders and in chronic diseases the following pathological processes take place:

• suppression of synthesis, increased catabolism or increased vascular permeability decrease albumin concentration
• increase in globulin concentration contributes to oncotic pressure. Hypergammaglobulinemia > 50 g/L potentially leads to underestimation of serum albumin gradient /1/.

References

1. Tay TY, Nordin N, Badaruddin IA, Othman H. A patient with third-space fluid loss. Clin Chem 2023; 69 (2): 125–9.

47.14 Saliva

Saliva is a fluid with a variety of biomolecules containing enzymes, metabolites, plasmaproteins, hormones, DNA, and RNA. Sample collection of saliva is non-invasive. A listing of biomarkers is shown under Reference /1/.

References

1. Huang Z, Yang X, Huang Y, Tang Z, Chen Y, Liu H, et al. Saliva – a new opportunity for fluid biopsy. Clin Chem Lab Med 2023; 61 (1): 4–12.