Detection of mycobacterial antigens in sputum by an enzyme immunoassay

An enzyme immunoassay (EIA) for the detection of mycobacterial antigens in sputum was evaluated. The system utilises commercially available anti-BCG immunoglobulin. BCG protein standard was used as positive control. Thirty-nine patients with culture-proven pulmonary tuberculosis were tested. The EIA was positive in 24 of 29 patients with positive smears and cultures, giving a sensitivity of 86.2%. It was also positive in six of ten patients with smear-negative culture-positive disease, resulting in a sensitivity of 60% in this group. In another 176 patients with different nontuberculous pulmonary infections, only nine were positive by EIA, giving a specificity of 94.9%. The high sensitivity and specificity of the assay make it a useful tool for the early diagnosis of pulmonary tuberculosis.