Molecular tests for tuberculosis are highly specific, so a positive result in a symptomatic patient is reliable. Sensitivity is lower in smear-negative disease, in people with HIV, and in children, who often cannot produce good sputum. When clinical suspicion stays high despite a negative result, send a second sample, request culture, consider other specimens such as induced sputum or gastric aspirate in children, and review the chest X-ray. Treatment can be started on clinical grounds when the picture is convincing.
- Trust a positive molecular result in a symptomatic patient.
- With a negative result and high suspicion, repeat the test and send culture.
- In people with HIV and in children, use additional specimens and tests.
- Treat empirically when the clinical and radiological picture is convincing.
Why it matters
Missed smear-negative TB keeps transmitting in the community.
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