ELISA test for tuberculosis

The Elisa test for diagnosis of tuberculosis using highly purified A 60 antigen extracted from mycobacteria was developed by Anda Biologicals, France, during the late 1980s. It is claimed to have about 95% sensitivity and specificity. Both IgG and IgM antibodies can be separately tested. IgM antibodies appear early in the disease and IgG appear later. The test is negative in healthy, normal subjects and is not related to tuberculin test or BCG vaccination status. The A 60 antigen is common to many mycobacteria including M. tuberculosis, M. leprae, M. bovis, and M. avium. Hence, clinical, radiological and other laboratory data must be considered along with the results of Elisa test for final diagnosis. Tuberculosis is still the most important bacterial infection in India. Because of its high prevalence, normal subjects and proved tuberculosis patients were first surveyed to determine the cut off values for IgG and IgM antibodies among local population. Subsequently the test was offered in India for general use. This paper describes our experience of the test since 1990, on samples referred by various practitioners and laboratories in Bombay and other cities. Result on 5840 IgG tests and 2101 IgM tests shows that the A 60 Elisa test is well accepted and is a useful laboratory aid in the diagnosis of pulmonary and extrapulmonary tuberculosis.