Serodiagnosis of tuberculosis using the A60 IgG ELISA

The serodiagnosis of tuberculosis (TB) by using an enzyme-linked immunosorbent assay (ELISA) to detect IgG against mycobacterial antigen 60 (A60) was evaluated. Forty-three controls (10 healthy adults, 19 patients with non-tuberculous pulmonary diseases and 14 patients with non-pulmonary infectious diseases) and 63 patients with TB in different disease activity (50 patients with active TB and 13 patients with old pulmonary TB) were studied. When a cut-off value of 200 units was selected, the results obtained with controls were: 100% negative in IgG titers in healthy adults and patients with non-pulmonary infectious diseases, 89% negative in IgG titers in patients with non-tuberculous pulmonary diseases. The overall "false positive" rate was 5% in the control groups. The percentage of serologically positive cases of active TB was: 82% in smear-positive, 67% in smear-negative/culture-positive and 38% in culture-negative. Of the 13 patients with calcified pulmonary TB, four had a positive serological response (31%). Four out of eight patients with active TB showed an elevation in IgG titer 1 to 3 months after diagnosis and anti-TB chemotherapy. The positive and negative predictive values of the test may provide valuable information according to the prevalence of TB in different populations. When the TB prevalence is high, a positive IgG ELISA test may support the diagnosis of active TB.