Serous fluids (pleural, peritoneal, pericardial)

11 ASCP MLS practice questions on Serous fluids (pleural, peritoneal, pericardial), part of Urinalysis and Body Fluids. The first 11 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 52-year-old man developed severe chest pain after repeated forceful vomiting following a heavy meal with alcohol. A left pleural effusion is tapped. Pleural fluid: protein 4.4 g/dL [44 g/L], LD 980 U/L, pH 6.6, amylase 2,400 U/L; small food particles and squamous epithelial cells are seen. Serum: protein 6.8 g/dL [68 g/L], LD 260 U/L (upper reference limit 222 U/L), amylase 95 U/L, lipase normal. Isoenzyme study shows that the pleural fluid amylase is mostly salivary type. The classification and most likely cause are:

   1. ATransudate from heart failure
   2. BExudate from acute pancreatitis
   3. CExudate from esophageal rupture
   4. DExudate from a parapneumonic infection

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   Answer: C · Exudate from esophageal rupture

   The fluid-to-serum protein ratio is 0.65 and the LD ratio is 3.8, and the fluid LD is above two-thirds of the serum upper limit (148 U/L), so all three of Light's criteria classify the fluid as an exudate. A pleural amylase far above the serum level narrows the cause to the pancreas, the esophagus or, less often, a tumor. Salivary-type amylase, a very low pH, food particles and squamous cells after forceful vomiting point to esophageal rupture (Boerhaave syndrome), which lets swallowed saliva and gastric contents into the pleural space. Pancreatitis would give pancreatic-type amylase with a raised serum lipase. Esophageal rupture is a surgical emergency, so the result should be reported at once.

   • A: All three of Light's criteria are met, so the fluid is an exudate, not a transudate.
   • B: Pancreatic effusions contain pancreatic-type amylase, and the serum lipase is normal.
   • D: Parapneumonic fluid does not contain salivary amylase, food particles or squamous cells.

2. Question 2 · Hard

   Pleural fluid from a patient with pneumonia has a glucose of 35 mg/dL (1.9 mmol/L) and an LD of 1,900 U/L. Its pH is 7.41 on a blood gas analyzer, but the fluid was sent in an open sterile cup. What is the best interpretation of the pH?

   1. AFalsely low from air exposure; correct for temperature
   2. BFalsely high from CO2 loss; repeat on an anaerobic sample
   3. CReliable, so chest tube drainage is not needed
   4. DFalsely high from glycolysis in the cup; add fluoride

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   Answer: B · Falsely high from CO2 loss; repeat on an anaerobic sample

   Pleural fluid for pH is collected anaerobically in a heparinized syringe, like an arterial blood gas, kept on ice and measured promptly. In an open cup, CO2 escapes into the air and the pH rises, so 7.41 is not reliable. The very low glucose and high LD suggest a complicated parapneumonic effusion, in which the true pH is often below 7.20, the cutoff that favors chest tube drainage. The sample should be recollected correctly rather than reported.

   • A: Loss of CO2 to air raises the pH; it does not lower it.
   • C: Air exposure makes the pH unreliable, and the low glucose and high LD suggest drainage may be needed.
   • D: Glycolysis produces acid and lowers pH; fluoride does not correct a CO2 loss.

3. Question 3 · Hard

   A 59-year-old man with cirrhosis has fever and abdominal tenderness. Ascitic fluid WBC is 700/µL (700 x 10^6/L) with 65% neutrophils. What is the absolute neutrophil count and its meaning?

   1. A455/µL; usual for uncomplicated cirrhosis
   2. B45,500/µL; secondary bacterial peritonitis
   3. C455/µL; spontaneous bacterial peritonitis
   4. D245/µL; below the threshold for infection

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   Answer: C · 455/µL; spontaneous bacterial peritonitis

   Absolute neutrophils = 700 x 0.65 = 455/µL (455 x 10^6/L). An ascitic neutrophil count of 250/µL or more in a patient with cirrhosis is diagnostic of spontaneous bacterial peritonitis, and antibiotics are started without waiting for culture. Inoculating fluid into blood culture bottles at the bedside raises the culture yield. The decision uses the neutrophil count, not the total WBC, because lymphocytes are common in uninfected ascites.

   • A: Uncomplicated cirrhotic ascites has fewer than 250 neutrophils/µL.
   • B: 45,500/µL comes from multiplying by 65 instead of 0.65.
   • D: 245/µL is the non-neutrophil fraction (35%), not the neutrophil count.

4. Question 4 · Medium

   A lymphocyte-rich pleural exudate with very few mesothelial cells is suspected to be tuberculous. Which fluid test best supports this?

   1. ATriglyceride
   2. BCarcinoembryonic antigen
   3. CAdenosine deaminase
   4. DAmylase

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   Answer: C · Adenosine deaminase

   Adenosine deaminase (ADA) is an enzyme of activated T lymphocytes and is high in tuberculous pleuritis, often above about 40 U/L. A lymphocytic exudate with few mesothelial cells adds to the suspicion, because the inflamed pleura is covered with fibrin. Acid-fast smears of pleural fluid are usually negative and culture takes weeks, so ADA gives a faster answer. ADA can also be raised in empyema and some lymphomas, so it is read with the clinical picture.

   • A: Triglyceride identifies a chylous effusion.
   • B: CEA supports a malignant effusion, especially from adenocarcinoma.
   • D: Amylase is raised in pancreatitis and esophageal rupture.

5. Question 5 · Medium

   Pleural fluid is evenly bloody in every tube, with a hematocrit of 26% (0.26 L/L); the blood hematocrit is 38% (0.38 L/L). How is this best classified?

   1. AMalignant effusion
   2. BHemothorax
   3. CPulmonary infarction
   4. DTraumatic tap

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   Answer: B · Hemothorax

   The fluid hematocrit is 26/38 = 0.68 of the blood hematocrit, more than half, which is the usual cutoff for a hemothorax. Bleeding into the pleural space after chest trauma, surgery or a ruptured vessel is the cause. Malignant effusions and pulmonary infarcts can look bloody, but their hematocrit is far below half the blood value. Blood that is even in all tubes argues against a traumatic tap, in which the blood decreases as collection goes on.

   • A: Malignant effusions can be bloody but have a much lower hematocrit.
   • C: Infarction can give a bloody effusion, but its hematocrit is far below half the blood value.
   • D: A traumatic tap gives blood that decreases from tube to tube.

6. Question 6 · Hard

   A 54-year-old man with ascites has a serum albumin of 2.9 g/dL (29 g/L) and an ascitic fluid albumin of 1.1 g/dL (11 g/L), collected on the same day. The serum-ascites albumin gradient and its meaning are:

   1. A4.0 g/dL (40 g/L); portal hypertension
   2. B0.38; exudate from peritoneal disease
   3. C1.8 g/dL (18 g/L); peritoneal carcinomatosis
   4. D1.8 g/dL (18 g/L); portal hypertension

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7. Question 7 · Easy

   A pleural transudate forms mainly because of:

   1. ABacteria spreading from the lung
   2. BA change in hydrostatic or oncotic pressure
   3. CTumor cells shed onto the pleural surface
   4. DInflammation that makes capillaries leaky

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8. Question 8 · Medium

   Milky pleural fluid from a patient who recently had esophageal surgery has a triglyceride of 420 mg/dL (4.74 mmol/L). This is most consistent with:

   1. ATransudate from heart failure
   2. BEmpyema from a bacterial infection
   3. CPseudochylous effusion from chronic pleuritis
   4. DChylothorax from thoracic duct injury

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9. Question 9 · Medium

   A pleural fluid has a fluid-to-serum protein ratio of 0.68 and a fluid-to-serum LD ratio of 0.82. The most likely cause is:

   1. AHepatic cirrhosis
   2. BBacterial pneumonia
   3. CCongestive heart failure
   4. DNephrotic syndrome

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10. Question 10 · Hard

    A 66-year-old woman has a pleural effusion. Fluid: protein 2.4 g/dL (24 g/L), LD 260 U/L. Serum: protein 7.0 g/dL (70 g/L), LD 290 U/L; the upper reference limit for serum LD is 222 U/L. How should the fluid be classified?

    1. ANot classifiable, because the criteria disagree
    2. BTransudate, because the protein ratio is 0.34
    3. CExudate, because the LD criteria are met
    4. DTransudate, because fluid LD is below serum LD

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11. Question 11 · Easy

    Light's criteria compare pleural fluid with serum for which two analytes?

    1. AAlbumin and cholesterol
    2. BGlucose and amylase
    3. CTriglyceride and bilirubin
    4. DProtein and lactate dehydrogenase

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