Diagnostic accuracy of Truenat MTB Plus, Truenat MTB Ultima and Xpert MTB/RIF Ultra for the diagnosis of pulmonary TB in an HIV-endemic setting.

Background

Truenat MTB Plus (MTB Plus) and MTB Ultima (Ultima) are World Health Organization-endorsed low-complexity tuberculosis (TB) tests, however, performance data are scarce.

Methods

Adults (≥18 years; n=498) self-presenting with symptoms to primary care clinics in Cape Town, South Africa (19/02/2016-22/02/2023) provided sputa. We evaluated the accuracy of MTB Plus and Ultima, with Xpert MTB/RIF Ultra (Ultra) as a comparator, vs. a single culture (TB reference standard) or MTBDR

Results

The proportion of MTB Plus and Ultima unsuccessful results was 20% (95% confidence interval 17, 23) and 14 (11, 16), respectively, with ≥half resolving upon retesting the same eluate. In a three-way analysis, MTB Plus, Ultima and Ultra had sensitivities of 84% (78, 88), 90% (85, 93), and 92% (87, 95), and specificities of 95% (92, 97), 85% (80, 88) and 95% (92, 97) for TB. The proportion of unsuccessful results for MTB-RIF Dx done the same day as DNA extraction was 9% (3, 16; MTB Plus-positives) and 18% (10, 26; Ultima-positives) [if after day-of-extraction, these were 27% (18, 35) and 44% (35, 51)]. Same-day rifampicin susceptibility testing was often unsuccessful in samples with "very low" load [73% (58, 89) MTB Plus, 75% (65, 86) Ultima] but had 100% (40, 100) sensitivity and 99% (96, 100) specificity (for both MTB Plus- or Ultima-positive DNA). Lot variation in unsuccessful and false-positive results was observed.

Conclusion

Ultima showed comparable sensitivity to Ultra but specificity, lot variation, and, like MTB-RIF Dx, unsuccessful result rates were suboptimal.

Funding

European & Developing Countries Clinical Trials Partnership, and South African Medical Research Council.

Déclaration de conflit d'intérêts

Declaration of interests We received in-kind donations of diagnostic test kits and equipment from Cepheid and Molbio. Cepheid and Molbio had no role in study design or interpretation of results. The authors have no financial involvement with any organisation or entity with a financial interest in, or financial conflict with, the subject matter or materials discussed in the manuscript apart from those disclosed.