Diagnostic accuracy of rK28-based immunochromatographic rapid diagnostic tests for visceral leishmaniasis: a prospective clinical cohort study in Sudan

Background Rapid diagnostic tests (RDTs) for visceral leishmaniasis (VL) based on rK39 antigen showed suboptimal sensitivity in East Africa. A prospective clinical cohort study in Sudan was designed to validate a novel rK28-based RDT for Leishmania donovani VL. Methods Patients (n=285) suspected of VL by residency, fever for ≥2 weeks, splenomegaly with no prior reported VL, and negative for malaria were consecutively enrolled at three Sudanese sites in 2012-2013 and informed consent obtained. Two human readers, who were blinded to the clinical status and other RDT results, evaluated patient whole blood (WB) and serum on the rK28 RDT. Based on Leishmania parasite detection in lymph node or bone marrow aspirates (Giemsa-stained smears or culture in Novy-MacNeal-Nicolle medium), patients were categorized as VL cases (n=200) or VL controls (n=85). Results The rK28 RDT had high specificity using either WB (100% [85/85]) or serum (97.6% [83/85]) and exhibited greater sensitivity (WB, 92.5% [185/200]; serum, 94.5% [189/200]) than a direct agglutination test performed with the same sera (92.9% [79/85] and 83.5% [167/200] for specificity and sensitivity, respectively). Two blinded readers scored a given WB or serum sample the same on the rK28 RDT 99.6% and 100% of the time, respectively. A reader scored each individual donor's paired WB and serum rK28 RDT results the same 97.2% of the time. Conclusions An inexpensive rK28 RDT that performs robustly with WB or serum will be valuable for diagnosing cases of VL in East Africa.