Serological diagnosis of Indian visceral leishmaniasis: direct agglutination test versus rK39 strip test

Abstract

We evaluated the direct agglutination test (DAT), using freeze-dried (FD) and aqueous (AQ) antigen, and the rK39 immunochromatographic strip test in the diagnosis of Indian visceral leishmaniasis (VL). Sera from 508 subjects (150 parasitologically confirmed patients with VL, 100 and 153 healthy controls drawn from non-endemic and endemic regions, respectively, and 105 patients with other diseases presenting with fever and/or splenomegaly) were tested. The sensitivity of the tests were as follows: DAT (FD), 96% (95% CI 91-98); DAT (AQ), 97% (95% CI 93-99); rK39 strip test, 99% (95% CI 95-100). The specificity of DAT (FD), DAT (AQ) and rK39 strip tests were 85% (95% CI 81-88), 87% (95% CI 83-91) and 89% (95% CI 86-92), respectively. A significant correlation (high degree of agreement) was observed between all tests (kappa>0.80). We conclude that the sensitivity of FD antigen is comparable to that of AQ antigen. Similarly, the rK39 strip test is as sensitive as the DAT, but the strip test's greater convenience of use makes it a better tool for diagnosis of VL in peripheral areas of endemic regions.