Development of a new antigen detection dot-ELISA for diagnosis of tubercular lymphadenitis in fine needle aspirates

A sandwich dot enzyme-linked immunosorbent assay (ELISA) was standardized to detect mycobacterial antigen in fine needle aspirates of patients with tubercular lymphadenitis (TBLN). The assay was performed on nitrocellulose paper by using antibodies raised in mice and rabbits against crude soluble protein (CSP) of Mycobacterium tuberculosis. The test was able to detect as low as 5 ng protein/ml. A total of 225 suspected cases of tubercular lymphadenopathy were screened, out of which 96 were cytomorphologically confirmed as cases of tubercular lymphadenitis (50 acid-fast bacilli (AFB)-positive and 46 AFB-negative). These were considered as positive controls. Only 28 cases were proven to be of nontubercular etiology and were considered as negative controls. In the remaining 101 (39 scanty) aspirates, tubercular etiology could neither be ruled out nor confirmed. Out of 50 AFB-positive confirmed cases of tubercular lymphadenitis, 46 were ELISA-positive. Out of 46 AFB-negative but cytomorphologically confirmed aspirates, antigen could be demonstrated in only 42 aspirates. Four samples from patients with nontubercular etiology were also found to be ELISA-positive. Antigen was picked up in a total of 90.3% of aspirates with suspicion of tuberculosis and 79.5% of scanty aspirates. The assay was found to be 91.6% sensitive and 85.7% specific. The assay was found to be simple and rapid, and hence, could be performed in areas where health facilities are rudimentary.