Evaluation of fluorescent leprosy antibody absorption test versus enzyme-linked immunosorbent assay with phenolic glycolipid 1 and their use in immuno-epidemiological studies on leprosy.

We systematically conducted comparative studies on the validity, reliability and practicality of FLA-ABS.T/PGI-ELISA in large samples. Namely, 284 leprosy patients, 20 tuberculosis patients, 172 normal controls (from nonendemic area of leprosy), 425 leprosy household contacts (HC) and 2573 random samples from the general population (RS) were involved. The results indicated that FLA-ABS.T/PGI-ELISA are highly sensitive and specific for detecting antibodies against M. leprae. Their Youden's indexes (YI) are greater than 90%, and the positive predicative and negative values are 90%. The test results agreed with immuno-epidemiological studies: 1. The positive rates using FLA-ABS.T/PGI-ELISA increased gradually from TT to LL leprosy patients (in HC, the positive rates of PGI-ELISA were much higher in contacts of multibacillary patients than in contacts of paucibacillary patients); 2. The positive rates detected by FLA-ABS.T were identical to those of PGI-ELISA both in HC and in RS; 3. Among RS, the positive rates detected by FLA-ABS. T/PGI-ELISA were similar in each district and were in concordance with the general prevalence rates. Thus, both FLA-ABS.T and PGI-ELISA are useful tests in diagnosing leprosy and detecting subclinical infection with M. leprae. However, because the PGI-ELISA is simple, it will be more practical than FLA-ABS.T in the future. The authors emphasize that the methodology of obtaining dried blood from ear lobes is important for the immuno-epidemiological study of leprosy on a large scale.