Evaluation of the Performance of Three Diagnostic Tests for Tuberculosis Among Hiv Patients Presenting to Kibra Community Health Center, Nairobi County, Kenya.

Abstract

Background- The absence of an accurate reference test complicates the evaluation of tuberculosis (TB) diagnostic tests among people living with Human Immunodeficiency Virus (PLWHIV). Verifiable evidence on performance of the routinely used diagnostic tests is key to inform early TB detection and population-based surveillance among PLWHIV. The objective of this study was to estimate the sensitivity (Se), specificity (Sp) and negative and positive predictive values (NPV and PPV) of sputum smear microscopy (SSM), Xpert Ultra and lipoarabinomannan antigen (LAM) tests for TB among PLWHIV in Nairobi County, Kenya. Methodology- This cross-sectional study enrolled a total of 190 patients aged ≥ 18 years with presumptive TB seeking treatment at the Kibra Community Health Center Comprehensive Care Centre (CCC) clinic between September 2022 and March 2023. The diagnostic data obtained from the three tests were analysed using a Bayesian latent class analysis framework to derive accuracy estimates of the three diagnostic tests. Results- The Xpert Ultra assay registered a higher Se (85.0; 95% PCI [41.4 – 99.4]) compared to LAM (26.8; 95% PCI [4.7 – 67.6]) and SSM (56.7 [16.4 – 97.4]). However, SSM had the highest Sp (99.6; 95% PCI [97.7 – 100.0]). The Xpert Ultra assay yielded the highest overall combination of Se and Sp at 80.8% (95% PCI [37.0 – 96.5]). On predictive values, SSM recorded the highest PPV at 84.5% (95% PCI [38.4 – 99.4]). Nonetheless, all the tests exhibited noticeably high NPVs (>96%). Conclusions- The Xpert Ultra assay recorded the highest Se of the three tests. However, SSM displayed the highest Sp and thus PPV estimate. Notwithstanding, the three tests registered similar NPV’s. An optimal testing approach in this low-prevalence TB setting could entail an initial screening with the more sensitive Xpert Ultra test, with any resultant positives retested with the more specific SSM test - a two-test serial testing strategy.