Detection of mycobacterial antigens in sputum by enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assay (ELISA) was evaluated for its usefulness in detecting mycobacterial antigens in sputum. Using anti-mycobacterial saline extract (MSE) and commonly available anti-bacillus Calmette Guerin (BCG) antibodies, Mycobacterium tuberculosis antigens can be detected in sputum by the double-antibody sandwich ELISA. A total of 1904 sputum specimens were tested by acid-fast bacillus (AFB) smear, culture and ELISA. Of 249 pulmonary tuberculosis patients, 225 (90.4%), 167 (67.1%), 114 (45.8%), 103 (41.4%) and (36.9%) were positive by BACTEC 460, 7H11 culture, AFB smear, BCG-ELISA and MSE-ELISA, respectively. If BACTEC 460 positive culture only is considered as the standard, sensitivity of 43.6% and 36.9%, and specificity of 98.2% and 98.3% are achieved, with positive predictive value of 76.0% and 74.1%, and negative predictive value of 92.8% and 92.1% for BCG- and MSE-ELISA, respectively. In 7H11 culture positive cases: 46.7% (BCG) and 43.1% (MSE) for sensitivity, 97.1% (BCG) and 97.7% (MSE) for specificity, 60.5% (BCG) and 64.3% (MSE) positive, 95% (BCG) and 94.7% (MSE) negative predictive values were achieved. When there is an urgent need the ELISA can serve as an alternative aid for the presumptive differentiation of other mycobacteria from M. tuberculosis.