Which investigation is considered as gold standard of to diagnosis Sputum microscopy Chest x ray Mycobacterial culture Mantoux test
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The answer is C. Mycobacterial culture.
Mycobacterial culture is the gold standard for the diagnosis of tuberculosis (TB). Multiple authoritative sources confirm this:
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"Culture in liquid media is considered the current diagnostic gold standard and can detect as few as 10 to 1000 viable mycobacteria/mL of sputum." — Murray & Nadel's Textbook of Respiratory Medicine
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"The gold standard for diagnosis is growth of M. tuberculosis in culture, typically within 1 to 3 weeks by modern testing methods." — Goldman-Cecil Medicine
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"Although culture remains the gold standard, PCR..." — Robbins, Cotran & Kumar Pathologic Basis of Disease
Why the other options are incorrect:
| Option | Role | Limitation |
|---|---|---|
| Sputum microscopy (AFB smear) | Rapid, inexpensive screening tool | Low sensitivity (~50–60%); cannot speciate or test drug sensitivity |
| Chest X-ray | Suggestive of pulmonary TB | Not specific; many conditions mimic TB on X-ray |
| Mantoux test (TST) | Detects TB exposure/latent infection | Cannot distinguish latent from active TB; false positives with BCG vaccination |
Culture allows definitive identification of Mycobacterium tuberculosis, species confirmation, and crucially — drug susceptibility testing (DST), which no other option provides.
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