Tuberculosis in advanced HIV — DTM&H MCQ

Correct answer: E — Sputum Xpert MTB/RIF as an initial diagnostic test

The correct answer is E, sputum Xpert MTB/RIF as an initial diagnostic test. In a person with advanced HIV (CD4 40 cells/mm3) and symptoms suggestive of pulmonary TB, rapid nucleic acid amplification testing (NAAT) such as Xpert MTB/RIF should be used on sputum as the first-line investigation, since it gives a result within hours, detects M. tuberculosis DNA directly, and simultaneously identifies rifampicin resistance. This is critical in advanced HIV because smear microscopy sensitivity is markedly reduced in paucibacillary disease, so relying on smear or waiting for slow culture risks missing or delaying diagnosis in a patient at high risk of rapid deterioration and death from untreated TB. NICE guidance mandates rapid NAAT testing on respiratory specimens for exactly this group of patients meeting specific risk criteria, including HIV positivity. Why the other options are wrong: C. Tuberculin skin test: this assesses immune sensitisation to mycobacterial antigen and cannot distinguish latent from active infection; it is also frequently false negative in advanced HIV due to anergy. B. Chest radiograph as the sole diagnostic test: imaging supports the diagnosis but is nonspecific, cannot confirm M. tuberculosis or rifampicin resistance, and must not be used alone to diagnose or exclude active TB. A. Wait for culture before assessing treatment: culture remains the reference standard for drug susceptibility but takes weeks, an unacceptable delay in a patient with advanced immunosuppression who needs urgent treatment decisions. D. Serum cryptococcal antigen as the TB test: this detects cryptococcal disease, an important differential in advanced HIV, but has no role whatsoever in diagnosing tuberculosis. Key point: In HIV-associated presumptive pulmonary TB, rapid molecular testing (Xpert MTB/RIF) on sputum is the recommended initial investigation because it is fast, sensitive even in paucibacillary disease, and detects rifampicin resistance simultaneously.

Reference: NICE. Tuberculosis quality standard QS141, quality statement 3: Rapid diagnosis of pulmonary tuberculosis (citing NICE guideline NG33, 2016, recommendations 1.3.3.1, 1.3.4.1-1.3.4.2, 1.4.1.1). https://www.nice.org.uk/guidance/qs141/chapter/quality-statement-3-rapid-diagnosis-of-pulmonary-tuberculosis