Performance of Three Tests for Tuberculosis among Human Immunodeficiency Virus (HIV) Patients Presenting to a Health Facility in an Informal Urban Settlement in Nairobi, Kenya.

The absence of an accurate reference test complicates the evaluation of tuberculosis diagnostic tests among people living with Human Immunodeficiency Virus (PLWHIV). Bayesian latent class models was utilized in the estimation of the sensitivity (Se), specificity (Sp) and negative and positive predictive values of sputum smear microscopy (SSM), Xpert Ultra and lipoarabinomannan (LAM) antigen tests for tuberculosis among HIV positive patients in Nairobi, Kenya.
This cross-sectional study enrolled a total of 190 patients aged ≥ 18 years with presumptive tuberculosis seeking treatment at the Kibra Community Health Centre, Comprehensive Care clinic (CCC), between September 2022 and March 2023.  The diagnostic data obtained from the three tests was analysed using a Bayesian latent class model framework to derive accuracy estimates of the three diagnostic tests.
The Xpert Ultra assay registered a higher Sensitivity (85.0%) compared to LAM antigen (26.8%) and SSM (56.7%). However, SSM had the highest Specificity (99. 6%).The Xpert Ultra assay yielded the highest overall combination of Sensitivity and Specificity at (80.8%).  Sputum smear microscopy recorded the highest positive predictive value (PPV) at (84.5%). Nonetheless, all the three tests exhibited noticeably high Negative predictive values (NPV) (>96%). 
The Xpert Ultra assay recorded the highest Sensitivity of the three tests., and the SSM test registered the highest Specificity and correspondingly the highest positive predictive value. The tests had similar Negative predictive value estimates. Consequently, a two-test serial testing strategy, entailing an initial screening with the more sensitive Xpert Ultra assay followed by retesting of any positives with the more specific sputum smear microscopy test, was considered to be most optimal in this low-burden tuberculosis setting to assure that false positive individuals are not unnecessarily subjected to protracted therapy for tuberculosis.