Haematological malignancies as disorders negatively impacting specificities of the direct agglutination and rapid rK39 strip tests as reference diagnostics for visceral leishmanisis

Abstract

Introduction. During several years of work in Sudan, we occasionally had been confronted with patients who presented clinical features highly suggestive of visceral leishmaniasis (VL) however direct agglutination test (DAT) readings that were either at the high negative or low positive titre range. Inquiries on the fate of those particular patients revealed mortality, undetermined diagnosis or that in some of them leukaemia was finally diagnosed. Gap statement. Investigate as to what extent haematological malignancies (HMs) interfere with VL diagnosis. Aim. Evaluate specificity of DAT version newly developed in this study wherein sodium dodecyle sulphate (SDS) was incorporated as a test sample denaturant in comparison with a standard reference wherein β-mercaptoethanol (β-ME) was used in test execution. Methodology. Seventy plasma samples from patients with HMs were collected and tested in a primary DAT version (P-DAT). The results obtained were compared with those of the rK39 strip test as VL reference diagnostic. HM samples revealing titres higher than the start dilution (1 : 100) in P-DAT were further tested in a β-ME- and urea-modified DAT versions. The specificity of the newly developed SDS-DAT was assessed against that of β-ME-DAT and rK39 strip tests as current reference diagnostics for VL. Results. Seven out of 70 patients with HMs scored positive outcomes (titre ≥1 : 3200) in P-DAT and four in the reference rK39 strip test. Of the seven that tested positive in P-DAT or four in the reference rK39, none reacted at titre >1 : 100 in the SDS-DAT. Significant reduction in non-specific agglutination reactions was achieved as a result in respect to the HM plasma samples (P value <0.05). Conclusion. To establish desired specificity for VL diagnosis in respect to HMs and subsequently minimize or avoid serious side effects due to unjustified anti-leishmanials prescription the combined application of the SDS-DAT here described and an improved version of the rK39 for confirmation is recommended.