Operational validation of the direct agglutination test for diagnosis of visceral leishmaniasis

The validity of the direct agglutination test (DAT) for visceral leishmania sis (VL) was studied with a standardized field kit on 148 clinically suspec ted persons and 176 healthy controls recruited between 1993 and 1994 from a n endemic area in Gedaref State, Sudan. A sensitivity of 95.9% and a specif icity of 99.4% were found at a 1:8,000 cut-off titer when parasitologically confirmed cases were compared with healthy controls. While corroborating p reviously reported sensitivity and specificity estimates of this serodiagno stic test, this study examined the bias generated by commonly used test val idation procedures. The fundamental methodologic problem in VL test validat ion is the absence of a reliable gold standard. Moreover, any operational g uideline on DAT use has to consider the critical dependency of the predicti ve values of the test on VL prevalence rates. The DAT diagnostic cut-off ti ter depends upon many external factors, among which the prevalence of disea se in the area and the case mix seem the most important.