Sero diagnosis of tuberculosis in children using two ELISA kits

The diagnosis of childhood tuberculosis is based on circumstantial evidence in the absence of a gold standard in the majority of cases. Sero-diagnosis offers scope for an early diagnosis in a variety of clinical conditions and is simple to perform. A number of mycobacterial antigens have been used for antibody detection assays and several are available as kits in the market. This study was done to evaluate the value of antibody detection kits (ELISA) against the A60 antigen and 38 kDa antigen of Mycobacterium tuberculosis in the diagnosis of childhood tuberculosis at the outpatient department of the Institute of Social Paediatrics, Government Stanley Hospital in collaboration with Tuberculosis Research Centre, Chennai. Thirty five children with pulmonary tuberculosis, 7 with TB lymphadenitis and 22 healthy controls were studied. In addition to routine investigations including gastric lavage for AFB culture, serum antibodies against the A60 and 38 kDa antigens were assayed using commercially available ELISA kits. With A60, IgM serum levels were positive in 74% of pulmonary TB cases, 57% of TB lymphadenitis cases and 50% of controls. A60 IgG was positive in 17% of pulmonary TB, 86% of TB lymphadenitis and 14% of controls. The 38 kDa IgG antibody was positive in 37% of pulmonary and 86% of TB lymphadenitis cases and 27% of controls. Among 10 culture confirmed cases, A60 IgM was positive in 8, A60 IgG in 3 and 38 kDa IgG in 5 patients. The sensitivity of the tests ranged between 29% and 71% and specificity between 50% and 86%. Although the numbers are small, the results suggest that serodiagnosis using the currently available antigens of M. tuberculosis is unlikely to be a confirmatory test for tuberculosis in children.