A multicenter evaluation of leprosy rapid test fast ML Flow hanseníase in Brazil

Abstract

Purpose Leprosy represents a public health concern; its diagnosis remains clinical. Recently, the Brazilian public health system/SUS incorporated the leprosy-specific IgM anti-PGL-I rapid test Fast ML Flow Hanseníase (MLFH/Bioclin, Brazil; originally ML Flow) to aid leprosy contacts surveillance and diagnosis. Anti-PGL-I antibody levels correlate with bacterial load. This multicenter study evaluated MLFH performance in confirmed leprosy cases from four Brazilian reference centers. Methods MLFH results were compared to anti-PGL-I ELISA, bacilloscopy/BI and analyzed in indeterminate/I, pure neuritic/PN and in Ridley Jopling/RJ categories (tuberculoid/TT, borderline-tuberculoid/BT, borderline/BB, borderline-lepromatous/BL, lepromatous/LL). Leprosy patients’ serum samples (N = 158; 95 multibacillary/MB, 63 paucibacillary/PB) were evaluated. Additionally, 20 previously tested leprosy samples were distributed to each center to assess MLFH repeatability, inter-center and inter-operator reproducibility. Results Higher MLFH seropositivity (84.8%) compared to ELISA (60.8%; p < 0.001) and bacilloscopy (50.6%; p < 0.001), indicated moderate and fair agreement, respectively. Visual intensity readings (0 to 4 + range) from 20 samples showed excellent agreement (ICC: 0.954); test repeatability was 95.57%. Compared to ELISA and bacilloscopy, positivity difference was statistically significant (p < 0.05) in TT, BT, and I forms. Lower MLFH positivity was observed in indeterminate, BT and PN forms. Conclusion The change in MLFH result criteria adopted by Bioclin/SUS considering faint test line (0.5) as positive (originally negative in ML Flow), increased MLFH sensitivity leading to higher seropositivity in MB and especially in PB, known as weak antibody producers. However, when screening asymptomatic leprosy contacts, this modified criterion may lead to reduced specificity since in endemic areas, anti-PGL-I positivity alone does not necessarily indicate active disease.