Evaluation of anti-A60 antigen IgG enzyme-linked immunosorbent assay for serodiagnosis of pulmonary tuberculosis

BACKGROUND: Problems in the diagnosis of tuberculosis using smear and culture techniques have necessitated the exploration of the utility of serodiagnosis to support clinical suspicion of tuberculosis. Anti-A60 antigen IgG enzyme-linked immunosorbent assay (ELISA) was evaluated as a tool for the diagnosis of active pulmonary tuberculosis. MATERIALS AND METHODS: ELISA was used for the detection of immunoglobulin G (IgG) against A60 antigen in parallel with other familiar diagnostic methods in 70 patients with pulmonary tuberculosis (Group_I) along with 70 controls showing evidence of latent tuberculosis infection (Group II). RESULTS: ELISA results were positive in 63 (90%) patients in Group_I compared to three (4%) controls in Group_II. Group_I patients had significantly higher titers of IgG (mean = 750.79 ± 115.87 U/ml against the A60 antigen as compared to Group II controls (mean = 206.67 ± 20.81 U/ml (P < 0.0001). The overall sensitivity and specificity obtained using ELISA were 90 and 95.7% respectively in active pulmonary tuberculosis. Ziehl-Nielsen (Z-N) stains for acid-fast bacilli were positive in 60 (85.7%) patients. In 48 (68.6%) patients, M. tuberculosis grew on both Lowenstein-Jensen (L-J) medium and BACTEC MGIT 960 liquid medium with mean detection times of 45 and 8 days respectively. Tuberculin skin test was positive in 38 (54.3%) patients. Chest X-ray results were consistent with the diagnosis of pulmonary tuberculosis in 53 (75.7%) patients. CONCLUSION: Anti-A60 IgG ELISA results were significantly positive and associated with elevated antibody titers in pulmonary tuberculosis as compared to latent mycobacterium infection. The high diagnostic performance of the test makes it a useful, simple and rapid supporting tool to validate clinical suspicion of active pulmonary disease.