LAUSR

ABSTRACT Background Serological tests for antibody measurement in leprosy have a series of limitations in discriminating contacts and patients. The present paper intends to evaluate if association of more than one antibody isotype in serum samples may be a useful tool in leprosy diagnosis. Methods This study evaluated 395 leprosy contacts and 71 leprosy index cases living in endemic municipalities in Northeastern Brazil. The participants were evaluated according to their anti-phenolic glycolipid antigen-I isotype (PGL-I) profile. Serum anti-PGL-I IgM, IgG, and IgA were measured by indirect ELISA. Results A strong association was found for antibody positivity in MB leprosy index cases. The odds ratios were 6.11 (95% CI 3.08 – 12.16) for IgM, 3.31 (1.66 – 6.61) for IgG, and 16.97 (8.39 – 34.2) for IgA. For IgM associated with one or more isotypes, the OR was 21.0 (95% CI 10.11 – 43.64), and for IgG + IgA, the OR was 17.58 (6.23 – 49.54). The highest diagnostic sensitivity of 76.0% (95% CI 61.8 – 86.9) was observed for IgM, and the lowest value was 24.1% (13.0 – 38.2), which was observed for IgG + IgA isotypes. Regarding presumptive positive predictive values, the lowest value was obtained for IgM at 24.7% (95% CI 18.1 – 32.3), and the highest values were observed for IgM+ one or more isotypes and for IgG + IgA isotype at 60.0% (44.3 – 74.3) and 66.7% (41.0 – 86.7), respectively. Conclusions The present work demonstrated that by associating two or more positive antibody isotypes, the risk of facing a real case of leprosy may increase.