A 45-year-old HIV-negative chronic cough patient from Kerala has sputum AFB smear-negative but GenXpert Ultra positive for Mycobacterium tuberculosis complex with RIF 'INDETERMINATE.' Sputum culture grows AFB at 6 weeks. What is the most appropriate next diagnostic step?

• A Request LPA (MTBDRplus) on the cultured isolate ✓
• B Repeat Xpert Ultra with fresh sputum sample and perform phenotypic DST simultaneously
• C Start MDR-TB treatment based on indeterminate RIF result
• D Perform IGRA (QuantiFERON-TB Gold Plus) to confirm active disease

Explanation

An indeterminate RIF result on Xpert Ultra means the probe inhibition pattern was equivocal—this is not equivalent to RIF resistance and should not trigger MDR-TB treatment. The appropriate step is LPA (MTBDRplus) on the culture isolate, which interrogates rpoB, katG and inhA simultaneously with high sensitivity and specificity. Repeating Xpert on fresh sputum is reasonable but may give the same indeterminate result. IGRA is used to diagnose latent TB infection, not active disease, and adds no value here.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.