Evaluation of antibody responses to panels of M. tuberculosis antigens as a screening tool for active tuberculosis in Uganda

BACKGROUND Improved systematic screening of high-risk groups is a key component of the tuberculosis (TB) elimination strategy endorsed by the World Health Organization (WHO). We used a multiplex microbead immunoassay to measure antibody responses to 28 M. tuberculosis (M.tb) antigens, and assessed whether combinations of antibody responses achieve accuracy thresholds required for a TB screening test. METHODS A random selection of plasma samples obtained from consecutive HIV-negative adults who were admitted to Mulago Hospital in Kampala, Uganda with cough ≥2 weeks' but <6 months' duration were analyzed for serological response to 28 M.tb antigens using an in-house multiplex microbead immunoassay. We compared the median difference of the antibody response to each antigen between patients with and without culture-confirmed TB, ranked each antigen according to variable importance (VIM), and assessed the sensitivity and specificity of combinations of antibody responses using an advanced classification algorithm, SuperLearner. RESULTS Among the 237 patients included in the analysis, 119 (50%) were female, median age was 32 years (IQR 25, 46), and 113 (48%) had TB. Median antibody levels to eight antigens were significantly different between patients with and without TB. A panel including eight of the top ranked antigens had a sensitivity of 90.6% (95% CI 89.4, 93.8) and a specificity of 88.6% (95% CI 78.2, 97.6) (Ag85B, Ag85A, Ag85C, Rv0934-P38, Rv3881, BfrB, Rv3873, and Rv2878c). With sensitivity constrained to be >90%, specificity remained close to 70% with as few as 3 antigens included in the panels. CONCLUSIONS Measuring antibody responses to combinations of antigens could facilitate TB screening and should be further evaluated in populations being targeted for systematic screening.