In a 60‑year‑old patient with dullness on percussion, low serum protein, high pleural protein, and pleural lactate dehydrogenase twice the serum level, which is the most likely cause of the pleural effusion: cirrhosis, congestive heart failure, tuberculosis, or hypoproteinemia?

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Tuberculosis is the Most Likely Cause

This pleural effusion is an exudate by Light's criteria, and tuberculosis (option C) is the most likely diagnosis among the choices provided.

Applying Light's Criteria to Classify the Effusion

The laboratory values demonstrate this is definitively an exudate based on Light's criteria 1:

  • Pleural fluid/serum protein ratio = 60/35 = 1.71 (>0.5 threshold → exudate)
  • Pleural fluid/serum LDH ratio = 200/100 = 2.0 (>0.6 threshold → exudate)
  • Both criteria are met, confirming exudative effusion 1

The effusion meets Light's criteria with values far exceeding the cutoff points, making this unequivocally an exudate rather than a transudate 1, 2.

Why the Answer Options Point to Tuberculosis

Among the four choices provided, only tuberculosis (C) causes exudative pleural effusions 1, 2, 3:

  • Cirrhosis (A) → causes transudative effusions (hepatic hydrothorax) 2, 3, 4
  • Congestive heart failure (B) → causes transudative effusions 1, 2
  • Hypoproteinemia (D) → causes transudative effusions 2, 3
  • Tuberculosis (C) → causes exudative effusions 1, 2, 3

Clinical Context Supporting Tuberculosis

The patient's age (60 years) and the presence of dullness on percussion with high pleural protein (60 g/L) and elevated pleural LDH (200 U/L) are consistent with tuberculous pleural effusion 1, 5. TB is the most common cause of exudative pleural effusion in TB-endemic areas and remains a leading cause globally 5.

Critical Pitfall to Avoid

Do not be misled by the low serum protein (35 g/L) into thinking this represents hypoproteinemia causing a transudate 1, 2. The pleural fluid protein/serum protein ratio of 1.71 definitively classifies this as an exudate regardless of the absolute serum protein level 1. Light's criteria use ratios precisely to avoid this error 1, 2.

Next Diagnostic Steps for Confirmation

To confirm tuberculous pleural effusion, measure pleural fluid adenosine deaminase (ADA) >40 U/L, which has high sensitivity and specificity for TB 3, 5. The pleural fluid LDH/ADA ratio <24 further supports TB over parapneumonic effusion 5. Consider pleural biopsy if ADA is equivocal 1, 3.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Differentiating Transudative from Exudative Pleural Effusion

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

3
Research

Management of pleural effusions.

Journal of the Formosan Medical Association = Taiwan yi zhi, 2000

4
Research

Evaluation of pleural fluid in patients with cirrhosis.

Journal of clinical gastroenterology, 1997

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