MCQs on Pleural Diseases

Written by Dr. Daniel Fraser (MBBS, FRACP) – Physician

Question 1

A 75-year-old man is admitted with increasing shortness of breath. He has a history of advanced prostate cancer with known bone metastases. Chest X-ray reveals a large right-sided pleural effusion. A diagnostic thoracentesis is performed. Pleural fluid analysis shows:

Pleural fluid protein: 46 g/L
Serum protein: 68 g/L
Pleural fluid LDH: 520 U/L
Serum LDH: 480 U/L

Which of the following best describes the classification of this pleural effusion?

A) Transudative by Light’s criteria
B) Exudative by Light’s criteria
C) Chylous effusion
D) Hemothorax
E) Empyema

Correct Answer: B) Exudative by Light’s criteria

Explanation:
To determine if a pleural effusion is exudative or transudative, Light’s criteria are applied. An effusion is exudative if any one of the following is true:

Pleural fluid protein / serum protein > 0.5
Pleural fluid LDH / serum LDH > 0.6
Pleural fluid LDH > 2/3 of the upper limit of normal serum LDH (typically ~200–300 U/L)

In this case:

Protein ratio = 46 / 68 = 0.68
LDH ratio = 520 / 480 = 1.08
Pleural fluid LDH = 520 U/L, well above 2/3 upper normal limit

All three criteria are met, classifying this as an exudative effusion.

Why the other options are incorrect:
A) Transudative – Does not meet Light’s criteria for transudate
C) Chylous effusion – Typically milky-white with high triglycerides
D) Hemothorax – Would show frank blood and pleural fluid hematocrit >50% of serum
E) Empyema – Purulent fluid with very high LDH and neutrophil predominance, usually with infection symptoms

Question 2

A 67-year-old man presents to the clinic with progressive shortness of breath and a dry cough for the past 3 weeks. He denies fever, chest pain, or hemoptysis. His medical history includes hypertension and congestive heart failure. On examination, he has decreased breath sounds and dullness to percussion over the right lower lung zone. There is no peripheral edema. A chest X-ray reveals a moderate right-sided pleural effusion. Diagnostic thoracentesis is performed, and the pleural fluid is straw-colored. Laboratory analysis shows:

Pleural fluid protein: 24 g/L
Serum protein: 72 g/L
Pleural fluid LDH: 120 U/L
Serum LDH: 300 U/L

Which of the following is the most likely cause of his pleural effusion?

A) Pulmonary embolism
B) Congestive heart failure
C) Tuberculous pleuritis
D) Bacterial pneumonia
E) Malignant pleural effusion

Correct Answer: B) Congestive heart failure

Explanation:
This patient has clinical signs and imaging consistent with a pleural effusion. The most likely etiology based on the presentation and pleural fluid analysis is a transudative pleural effusion secondary to congestive heart failure (CHF).

To differentiate transudate vs exudate, Light’s criteria are used:
Pleural fluid is exudate if at least one of the following is true:

Pleural fluid protein / serum protein > 0.5
Pleural fluid LDH / serum LDH > 0.6
Pleural fluid LDH > 2/3 of the upper limit of normal serum LDH

In this case:

24/72 = 0.33
120/300 = 0.4
120 U/L is below 2/3 of the upper limit of normal (typically ~200 U/L)

Thus, this is a transudate, pointing toward CHF, especially with supporting clinical history.

Why the other options are incorrect:
A) Pulmonary embolism – Typically causes exudative effusion; often associated with pleuritic chest pain or hemoptysis.
C) Tuberculous pleuritis – Exudative, usually with lymphocyte predominance and constitutional symptoms.
D) Bacterial pneumonia – Leads to parapneumonic effusion (exudative) with fever and purulent fluid.
E) Malignant pleural effusion – Exudative, often blood-stained, recurrent, and associated with weight loss or known malignancy.

Question 3

A 58-year-old woman presents with progressive shortness of breath and left-sided chest discomfort for the past two weeks. She denies fever, cough, or recent illness. Her past medical history includes rheumatoid arthritis and chronic kidney disease. On examination, she has reduced chest expansion on the left, stony dullness to percussion, and decreased breath sounds over the left lower zone. Chest X-ray shows a large left-sided pleural effusion. Thoracentesis yields cloudy, yellow fluid. Laboratory results are as follows:

Pleural fluid protein: 42 g/L
Serum protein: 70 g/L
Pleural fluid LDH: 360 U/L
Serum LDH: 450 U/L
Pleural fluid glucose: 2.2 mmol/L
Pleural fluid pH: 7.15

Which of the following is the most likely underlying cause of this patient’s pleural effusion?

A) Nephrotic syndrome
B) Cirrhosis
C) Rheumatoid arthritis
D) Congestive heart failure
E) Hypoalbuminemia

Correct Answer: C) Rheumatoid arthritis

Explanation:
This patient has a left-sided pleural effusion with exudative features on fluid analysis. The pleural fluid shows high protein, elevated LDH, low glucose, and low pH, which are classic features of a rheumatoid pleural effusion.

Light’s criteria confirm that this is an exudate:

Pleural fluid protein / serum protein = 42/70 = 0.6
Pleural fluid LDH / serum LDH = 360/450 = 0.8

These values exceed the thresholds for an exudative effusion.
Rheumatoid pleuritis typically presents with:

Very low glucose (<3.3 mmol/L, sometimes <1 mmol/L)
Low pH (<7.2)
High LDH
Straw-colored or cloudy fluid

Why the other options are incorrect:
A) Nephrotic syndrome – Usually causes transudative effusions, often bilateral, with low protein and normal pH/glucose.
B) Cirrhosis – Causes hepatic hydrothorax, a transudate, typically on the right side.
D) Congestive heart failure – A common cause of transudative effusions, usually bilateral or right-sided.
E) Hypoalbuminemia – Leads to transudative effusions due to reduced oncotic pressure; pleural fluid is low in protein.

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3. Respiratory Module

3.1 Asthma & COPD

3.2 Pulmonary Vascular Diseases

3.3 Pleural Diseases

3.4 Lung Cancer

3.5 Other Lung Diseases