Evaluation of the A-60 IgG ELISA serodiagnostic test for tuberculosis in Taiwan

To assess the applicability of a serologic test of specific IgG antibody for tuberculous infection in the Taiwan population, serum samples obtained from 118 subjects were analyzed by an ELISA test using mycobacterial antigen 60. There were 50 patients with a documented active infection caused by Mycobacterium tuberculosis (39 pulmonary tuberculosis, five pleurisy, three cervical lymphadenitis and three miliary tuberculosis with extrapulmonary involvement). Of these 50 patients, 42 (84%) showed a positive ELISA test (titer > 200 U). Of the 19 patients with inactive pulmonary tuberculosis, seven (37%) had a positive titer. Of the 22 patients with pulmonary disease other than tuberculosis, four (18%) showed a false-positive. In eight patients with autoimmune diseases, only the patient with rheumatoid arthritis had a positive reaction. One of the 19 healthy controls (5.3%) showed a false-positive result. The overall false-positive rate for the nontuberculous group was 12%. Follow-up examinations in 20 patients with active tuberculosis one month after treatment revealed that seven had an elevation in titers (three of them were initially negative and became positive later), five remained high and eight decreased in titers. Further examinations in six patients two months after treatment showed a decrease in titers. We conclude that this ELISA assay of specific IgG antibody is a valuable serologic test for diagnosis of M. tuberculosis infection. It may be useful in areas with a high prevalence of M. tuberculosis infection.