Xpert MTB/RIF Ultra is highly sensitive for the diagnosis of tuberculosis lymphadenitis in an HIV-endemic setting

Abstract

AbstractBackgroundTuberculosis lymphadenitis (TBL) is the most common extrapulmonary TB (EPTB) manifestation. Xpert MTB/RIF Ultra (Ultra) is a World Health Organization-endorsed diagnostic test, but performance data for TBL, including on non-invasive specimens, are limited.MethodsFine needle aspiration biopsies (FNABs) from outpatients (≥18 years) with presumptive TBL (n=135) underwent: 1) routine Xpert (later Ultra once programmatically available), 2) a MGIT960 culture (if Xpert- or Ultra-negative, or rifampicin-resistant), and 3) study Ultra. Concentrated paired urine underwent Ultra. Primary analyses used a microbiological reference standard (MRS).ResultsIn a head-to-head comparison (n=92) of FNAB study Ultra and Xpert, Ultra had increased sensitivity [91% (95% confidence interval 79, 98) vs. 72% (57, 84); p=0.016] and decreased specificity [76% (61, 87) vs. 93% (82, 99); p=0.020], and detected patients not on treatment. HIV nor alternative reference standards affected sensitivity and specificity. In patients with both routine and study Ultras, the latter detected more cases [+20% (0, 42); p=0.034] and, further indicative of potential laboratory-based room-for-improvement, false-negative study Ultras had more PCR inhibition than true-positives. Study Ultra “false-positives” had less mycobacterial DNA than “true-positives” [trace-positive proportions 59% (13/22) vs. 12% (5/51); p<0.001]. Exclusion or recategorization of “traces” removed potential benefits offered over Xpert. Urine Ultra had low sensitivity [18% (7, 35)].ConclusionsUltra on FNABs is highly sensitive and detects more TBL than Xpert. Patients with FNAB Ultra-positive “trace” results, most of whom will be culture-negative, may require additional clinical investigation. Urine Ultra could reduce the number of patients needing invasive sampling.