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

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Abstract
Summary: 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 (κ = 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 (κ = 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.

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