Diagnostic potential of 16 kDa (HspX, α-crystalline) antigen for serodiagnosis of tuberculosis

BACKGROUND & OBJECTIVES: Tuberculosis (TB) is a public health problem worldwide. Rapid and accurate diagnosis of tuberculosis is crucial to facilitate early treatment of infectious cases and to reduce its spread. The present study was aimed to evaluation of 16 kDa antigen as a serodiagnostic tool in pulmonary and extra-pulmonary tuberculosis patients in an effort to improve diagnostic algorithm for tuberculosis. METHODS: In this study, 200 serum samples were collected from smear positive and culture confirmed pulmonary tuberculosis patients, 30 tubercular pleural effusions and 21 tubercular meningitis (TBM) patients. Serum samples from 36 healthy, age matched controls (hospital staff), along with 60 patients with non-tubercular respiratory diseases were also collected and evaluated. Humoral response (both IgG and IgA) was looked for 16 kDa antigen using indirect ELISA. RESULTS: Sensitivity of detection in various categories of pulmonary TB patients ranged between 73.8 and 81.2 per cent. While in the extra-pulmonary TB samples the sensitivity was 42.8 per cent (TBM) and 63.3 per cent (tubercular pleural effusion). The test specificity in both the groups was high (94.7%). All of the non-disease controls were negative. Among non-tubercular disease controls, five patients gave a positive humoral response against 16 kDa. INTERPRETATION & CONCLUSIONS: Serodiagnostic tests for TB have always had drawbacks of suboptimal sensitivity and specificity. The antigen used in this study gave encouraging results in pulmonary TB only, while in extra-pulmonary TB (tubercular meningitis and tubercular pleural effusion), this has shown a limited role in terms of sensitivity. Further work is required to validate its role in serodiagnosis of TB especially extra-pulmonary TB.