A 62-year-old woman with type 2 diabetes mellitus presents with a 3-week history of low-grade fever, weight loss, and a right-sided pleural effusion. Thoracentesis shows exudative effusion (protein 5.4 g/dL, LDH 420 IU/L), lymphocyte predominance (85% lymphocytes), ADA (adenosine deaminase) 72 U/L. Pleural fluid AFB smear is negative. The MOST likely diagnosis and diagnostic test to confirm it is:

• A Tuberculous pleuritis; CBNAAT (Xpert MTB/RIF) of pleural fluid or pleural biopsy for AFB culture and histopathology (caseating granulomas) ✓
• B Malignant pleural effusion; CT-guided pleural biopsy for malignant cells
• C Parapneumonic effusion; blood culture for bacterial pathogen
• D Chylous effusion; measure pleural triglyceride level

Explanation

Lymphocyte-predominant exudative pleural effusion with elevated ADA > 40–50 U/L (here 72 U/L) in the appropriate clinical context (low-grade fever, weight loss, diabetic/immunocompromised host) is highly suggestive of tuberculous pleuritis. AFB smear of pleural fluid has low sensitivity (~20–40%) so negativity does not exclude TB. The diagnostic gold standard is pleural biopsy showing caseating granulomas plus AFB culture (>80% sensitivity combined). CBNAAT (Xpert MTB/RIF Ultra) on pleural tissue significantly improves sensitivity. India-ink staining and galactomannan would evaluate for fungal aetiologies.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.