Standardization of a dot blot immunoassay for antigen detection in cases of pulmonary tuberculosis & its evaluation with respect to the conventional techniques.

ABSTRACT

A simple dot (blot) ELISA test for detecting tubercular antigen in sputum samples of patients of pulmonary tuberculosis has been standardized using nitrocellulose paper. The sensitivity of the assay is 20 ng/ml. The cut-off value was 80 ng/ml. Of the 1042 patients in the study group, the percentage positivity by smear and culture was 54.51 and 57.93 per cent respectively; 68.7 per cent of the ELISA positives were confirmed by smear. The dot blot ELISA could be used as a rapid and specific test as it not only picked up 88.88 per cent of the smear positive, culture positive cases but also 81.89 per cent of the smear negative, culture positive cases. If the results of smear and dot blot ELISA are combined, 91.08 per cent of the culture positive cases were picked up as positive. If such a noninvasive test is commercialized and used in conjunction with smear, the pick up rate of tuberculosis cases will improve considerably.