Diagnostic accuracy study of a novel blood-based assay for identification of TB in people living with HIV.

A non-sputum triage test to rule out TB disease is a WHO high-priority diagnostic and a combinatory score based on a 3-gene host-signature has shown promise in discriminating TB from other illnesses. We evaluated the accuracy of an early-prototype cartridge-assay ("Xpert MTB Host Response", or Xpert-MTB-HR-Prototype) of this 3-gene signature on bio-banked blood-samples from PLHIV against a comprehensive microbiological reference standard (CMRS) and against Xpert® MTB/RIF on first sputum alone. We depict results based on performance targets set by WHO in comparison with a laboratory-based CRP assay. Of 201 patients included, 67 were culture-positive for Mycobacterium tuberculosis AUC for the Xpert-MTB-HR-Prototype was 0·89 (CI 0·83-0·94) against the CMRS and 0·94 (CI 0·89-0·98) against Xpert MTB/RIF. Considering Xpert-MTB-HR-Prototype as a triage test (at nearest upper value of sensitivity to 90%), specificity was 55·8% (CI 47·2-64·1) compared to the CMRS and 85·9% (CI 79·3-90·7) compared to Xpert MTB/RIF as confirmatory tests. Considering Xpert-MTB-HR-Prototype as a stand-alone diagnostic test, at a specificity near 95%, the test achieved a sensitivity of 65·7% (CI 53·7-75·9) while CRP achieved a sensitivity of only 13·6% (CI 7·3-23·4). In this first accuracy study of a prototype blood-based host-marker assay, we show the possible value of the assay for triage and diagnosis in PLHIV.