Evaluation of complement fixation procedures for the diagnosis of visceral leishmaniasis.

Three complement fixation (CF) procedures were evaluated for their ability to detect serum antibodies to visceral leishmaniasis. These tests differ in their use of buffers, volumes of complement and sensitized erythrocyte concentrations, incubation times and percentage haemolysis endpoints. Freeze-thawed sonicates of Leishmania donovani promastignotes were used as antigen. Test sensitivity was determined using sera from 46 Kenyans with parasitologically proven leishmaniasis. The frequencies of positive reactions in all three tests were 96-97% and positive antibody titres ranged from 1:16 to 1:4096. Specificity was determined with 20 sera from healthy individuals with no known exposure to leishmaniasis. The frequencies of false positive reactions were 0-10% in the control sera, with titres up to 1:16. No cross-reactions were observed with sera from patients with bacterial, fungal and other parasitic diseases. In replicate experiments, 99-100% of the sera tested were within one titre dilution of each other. All three CF procedures provide very good sensitivity, specificity and low cross-reactivity and are statistically similar in their capacity to diagnose visceral leishmaniasis.