Leishmaniasis Direct Agglutination Test: Using Pictorials as Training Materials to Reduce Inter-Reader Variability and Improve Accuracy

Background: the direct agglutination test (dat) has a high diagnostic accuracy and remains,in some geographical areas,part of the diagnostic algorithm for visceral leishmaniasis (vl). however,subjective interpretation of results introduces potential for inter-reader variation. we report an assessment of inter-laboratory agreement and propose a pictorial-based approach to standardize reading of the dat. methodology: in preparation for a comparative evaluation of immunochromatographic diagnostics for vl,a proficiency panel of 15 well-characterized sera,dat-antigen from a single batch and common protocol was sent to nine laboratories in latin-america,east-africa and asia. agreement (i.e.,equal titre or within 1 titer) with the reading by the reference laboratory was computed. due to significant inter-laboratory disagreement on-site refresher training was provided to all technicians performing dat. photos of training plates were made,and end-titres agreed upon by experienced users of dat within the visceral-leishmaniasis laboratory-network (vl-ln). results: pre-training,concordance in dat results with reference laboratories was only 50%,although agreement on negative sera was high (94%). after refresher training concordance increased to 84%; agreement on negative controls increased to 98%. variance in readings significantly decreased after training from 3.3 titres to an average of 1.0 titre (two-sample wilcoxon rank-sum (mann-whitney) test (z = -3,624 and p = 0.0003)). conclusion: the most probable explanation for disagreement was subjective endpoint reading. using pictorials as training materials may be a useful tool to reduce disparity in results and promote more standardized reading of dat,without compromising diagnostic sensitivity. © 2012 adams et al.