Comparative evaluation of parasitology and serological tests in the diagnosis of visceral leishmaniasis in India: a phase III diagnostic accuracy study

In this phase III trial for diagnostics for visceral leishmaniasis (VL) in India, we compared parasitological diagnosis with several serological tests: direct agglutination test (freeze dried; DAT-FD), rK-39 strip test, rK-26 strip test and a latex agglutination test for antigen detection in urine (KAtex) in 452 subjects from the endemic regions of Bihar, India. The subjects were segregated into four categories: 230 confirmed patients, 52 probable cases, 70 non-cases and 100 healthy endemic controls. The first two groups were used for estimating sensitivity, the latter two for specificity. Sensitivity of DAT-FD was 98.9%, rK-39: 98.9%, KAtex: 67.0% and rK-26: 21.3%. Sensitivity of DAT-FD on blood taken on filter paper (DAT-FDF) was 99.3%, which was comparable with that using serum. Specificity of serological tests was comparable and high (DAT-FD and DAT-FDF: 94%, rK-39 strip test: 97%, KAtex: 99% and rK-26 strip test: 100%). The classical 'gold standard' parasitological demonstration in splenic smear performed poorly as it missed 18.4% of cases that benefited from VL treatment. Reproducibility of the serological tests between field and central laboratories was excellent (kappa = 1.0, 0.99, 0.96 and 0.94 respectively for microscopy, DAT-FD, rK-39 strip test and rK-26 strip test). A high degree of agreement was observed between DAT-FD and rK-39 strip test (kappa = 0.986). Although DAT-FD and rK-39 strip test were highly sensitive with excellent specificity, the ease of use of the latter makes it most suitable for the diagnosis of VL in the field conditions.