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Sarcoidosis BAL CD4/CD8 — RACP Adult Medicine MCQ

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ModerateRespiratorySarcoidosis BAL CD4/CD8RACP Adult Medicine

A 48-year-old man presents with bilateral hilar lymphadenopathy, erythema nodosum, and acute polyarthralgia of the ankles. He also has bilateral anterior uveitis. His serum calcium is 2.85 mmol/L. What is the expected finding on bronchoalveolar lavage in sarcoidosis?

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Correct answer: C — Lymphocyte predominance with elevated CD4/CD8 ratio

BAL in sarcoidosis characteristically shows lymphocytic alveolitis with an elevated CD4/CD8 ratio (typically >3.5:1 – reflecting the Th1 predominant immune response in sarcoid granulomas). This is in contrast to hypersensitivity pneumonitis (which shows lymphocytosis but with a LOW CD4/CD8 ratio, <1.0, reflecting the CD8+ T-cell response). A CD4/CD8 ratio >3.5 has ~55% sensitivity and ~95% specificity for sarcoidosis. While BAL CD4/CD8 ratio alone is insufficient for diagnosis, it supports the clinical/histological diagnosis when combined with non-caseating granulomas on biopsy.

Reference: eTG – 2025 – Respiratory