Near point-of-care TB NAAT: good specificity, lower sensitivity than Xpert Ultra

Design

Cochrane systematic review and diagnostic accuracy meta-analysis

Population

5 studies, 3,291 people with presumptive pulmonary TB in 9 moderate- to high-burden countries

Primary outcome

Sensitivity and specificity against culture

Effect

Sensitivity 85.4% (95% CI 82.2 to 88.1); specificity 97.6% (95% CI 96.9 to 98.1)

This Cochrane systematic review, supported by WHO, assessed a new class of tuberculosis test: battery-operated nucleic acid amplification tests that can run outside a conventional laboratory with basic training. Five studies with 3,291 participants from nine moderate- to high-burden countries met the criteria, and all evaluated the same single device that meets the WHO class definition, using sputum.

Against culture, pooled sensitivity was 85.4% (95% CI 82.2 to 88.1) and specificity 97.6% (95% CI 96.9 to 98.1), moderate-certainty evidence. Among 1,000 symptomatic people of whom 100 have TB, that means about 15 missed cases and 22 false positives. Sensitivity was 79.2% in people with HIV and 66.7% in smear-negative, culture-positive disease. Head to head, it was about 7.5 percentage points less sensitive than Xpert MTB/RIF Ultra with similar specificity, and 22 points more sensitive than smear microscopy.

The certainty was downgraded because most testing happened in laboratories, not in the peripheral settings the test is designed for. Only one study included children, and none of them had confirmed TB. For laboratories and programmes, the result places the test above smear and below cartridge-based NAATs: a possible replacement for smear at sites that cannot run Xpert, not a substitute where Xpert is available.

• Treat this near point-of-care NAAT as more sensitive than smear microscopy but less sensitive than Xpert MTB/RIF Ultra.
• Consider it where only smear microscopy is currently available.
• Do not use a negative result to exclude TB in people with HIV or smear-negative presentations; send for a more sensitive test or culture.
• Note that evidence in children is essentially absent.
• Check national programme guidance before introducing it; adoption depends on algorithms and supply, not accuracy alone.

Why it matters

It is the first systematic evidence on a molecular TB test designed for sites without laboratory infrastructure, which describes much of rural India.

Don't overread it

Most studies ran the test in laboratories; accuracy at peripheral sites with less experienced operators may be lower.

The statistics, in plain English

Sensitivity of 85% means about 15 of every 100 people with culture-positive TB test negative. Specificity of 97.6% means about 2 or 3 of every 100 without TB test positive. The comparison with Xpert Ultra (-7.5 points, 95% CI -11.6 to -3.5) stays below zero, so the sensitivity gap is unlikely to be chance.

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