Filter paper blood spot test for detection of anti-ND-BSA antibodies in school children.

For identifying individuals at 'high risk' for developing leprosy, a simplified technique of collection of blood samples on filter paper for detection of anti -ND-BSA antibodies, was optimised. Anti-ND-BSA antibody reactivity on the filter paper was lost on storage at room temperature, but was stable at least for a period of 8 wk at lower temperature. Among the 1495 children screened, 166 (11.1%) were lepromin negative and 122 (8.2%) positive for anti-ND-BSA antibody. In the first phase, 7 of 871 children followed up for 2 yr developed leprosy, while in the second phase 2 of 624 children followed-up for 9 yr developed leprosy. The positivity and negativity of anti-ND-BSA antibodies and lepromin in these I children indicate that the positive status for anti-ND-BSA antibodies has a better predictive value than negative lepromin reactivity. Measurement of anti-ND-BSA antibodies was also of value for monitoring the efficacy of therapy and course of the disease. Extrapolation of the two tests to the total population of children evaluated showed that an individual with negative lepromin reactivity along with presence of anti-ND-BSA antibodies is at a higher risk for developing leprosy than those who have both the tests normal. Lepromin reactivity alone was not of much value for the prediction for development of the disease. However, the presence of anti-ND-BSA antibody was a better indicator for the development of the disease. The probability of developing leprosy in a child with any one of the tests abnormal was higher as compared to a child having all the tests normal.