The latex agglutination test: standardization and comparison with direct agglutination and dot-ELISA in the diagnosis of visceral leishmaniasis in India.

Laboratory diagnosis of visceral leishmaniasis (VL) is usually based on the detection of Leishmania amastigotes in samples of bone marrow or splenic aspirate obtained by invasive procedures. Serological tests serve as a useful adjunct and are especially valuable in early or highly immune cases where amastigotes may be too scanty to be seen easily. The direct agglutination test (DAT) is generally considered the most suitable of the four types of tests currently employed (IFAT, counter immuno-electrophoresis, ELISA and DAT). However, the latex agglutination test (LAT) was recently reported to be a rapid and sensitive screening tool for VL and one which could be carried out at the patient's bedside. Further standardization and evaluation of LAT has now revealed that although it is comparable with DAT and dot-ELISA in terms of sensitivity it is far inferior because of cross-reactivity with other infections. This lack of specificity makes LAT unsuitable for routine diagnosis of VL even though it is rapid and sensitive. DAT still appears to be the best choice as a diagnostic tool, as it is very specific and does not require expensive equipment or reagents or much technical competence and the result can be visually interpreted. These merits make DAT very suitable for the diagnosis of VL in endemic areas of India.