Role of antigen specific circulating immune complexes in diagnosis of tuberculosis

Setting: Tuberculosis is a public health problem worldwide. Early accurate diagnosis in patients with active disease is essential to reduce morbidity and mortality. Conventional methods for detection of Mycobacterium tuberculosis have given disappointing results.

Objective: To evaluate the utility of detection of M. tuberculosis antigen in circulating immune complexes (CIC) for the diagnosis of tuberculosis.

Method: Eighty-four clinically diagnosed cases of mainly extra-pulmonary tuberculosis, 85 patients with diseases other than tuberculosis and 30 healthy controls, were evaluated for the presence of antigen of M. tuberculosis in CIC in serum using sandwich enzyme linked immunosorbent assay (ELISA).

Results: In total, 22 out of 84 cases were positive for culture on Lowenstein Jensen medium; 76.5% (n = 65) of the clinically diagnosed patients (including 20 culture-positive cases) were found to be positive by ELISA. The difference in mean absorbance values of ELISA in cases of tuberculosis was significantly higher than in controls. The sensitivity of ELISA was 90.9% and the specificity was 93.04%.

Conclusion: Detection of M. tuberculosis antigen in CIC by ELISA has potential as a useful diagnostic tool for the rapid diagnosis of tuberculosis, especially extra-pulmonary forms where results of conventional methods of diagnosis are disappointing.