Tuberculosis Pathology MCQ — NEET PG Practice Question | NEETPGAI
Tuberculosis Pathology
hard
microscope Pathology
A 28-year-old woman with HIV/AIDS (CD4 count 45 cells/μL) presents with fever, cough, and dyspnea. Sputum smear microscopy is negative for acid-fast bacilli on two occasions. Chest X-ray shows bilateral interstitial infiltrates. Clinical suspicion for TB remains high. Which investigation is most appropriate to establish TB diagnosis in this immunocompromised patient?
A. GeneXpert MTB/RIF on sputum sample
B. Sputum culture on Löwenstein-Jensen medium alone, without waiting for smear results
C. Tuberculin skin test (TST) with 5 IU intradermal injection
D. Repeat sputum smear microscopy with fluorescent microscopy
Explanation
Investigation of Choice in Smear-Negative, Immunocompromised TB
Key Point
GeneXpert MTB/RIF (Xpert MTB/RIF) is the WHO-recommended rapid molecular test for TB diagnosis in smear-negative cases, especially in HIV-positive patients with low CD4 counts. It detects TB DNA and rifampicin resistance simultaneously within 2 hours.
Why GeneXpert MTB/RIF in This Scenario?
High-YieldNEET PG
In severely immunocompromised patients (CD4 < 50 cells/μL):
Sputum smear microscopy has low sensitivity (~30–40%) due to minimal inflammatory response and low bacillary load
TB may be present in extrapulmonary sites (lymph nodes, blood, CSF)
Rapid diagnosis is critical to initiate TB-HIV co-treatment early
GeneXpert MTB/RIF sensitivity is 95–98% even in smear-negative cases
Table
Investigation
Sensitivity (CD4 < 50)
Time to Result
Detects Resistance
Use in HIV+
Sputum smear microscopy
30–40%
1 day
No
Low
GeneXpert MTB/RIF
95–98%
2 hours
RIF resistance only
Recommended
Sputum culture
80–90%
2–8 weeks
Yes (full DST)
Yes, but slow
TST
<5% (anergic)
48–72 hours
No
Not reliable
Clinical Pearl
In HIV+ patients with CD4 < 100 cells/μL, TB-HIV co-infection mortality is high if TB diagnosis is delayed. GeneXpert MTB/RIF enables same-day diagnosis and rapid initiation of therapy.
Mnemonic — Diagnostic Approach in Smear-Negative TB:GRAM
GeneXpert MTB/RIF → first-line rapid test
Repeat smear (fluorescent microscopy) → if GeneXpert unavailable
Advanced imaging (HRCT) → assess extent
Molecular/culture → confirm and get DST
Warning
TST is unreliable in CD4 < 200 cells/μL due to anergy (cutaneous immune suppression). A negative TST does NOT exclude TB in this patient.
Harrison 21e Ch 165; WHO TB Guidelines 2023
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