False positive latex tests negative by ELISA for toxoplasma IgG.

An enzyme linked immunosorbent assay (ELISA) kit for detecting IgG class antibody to T gondii was compared with the latex agglutination test to determine the specificity as a screening method in 12 patients who had undergone heart transplantation (recrudescence of T gondii infection n = 3, donor acquired infection n = 3; acute cytomegalovirus infection n = 6). The latex agglutination test detected antibodies to primary T gondii infection much earlier in the infection than the ELISA, but the ELISA method was useful for detecting previous infection. It is concluded that the ELISA technique is more complex to perform than the latex agglutination test but the use of IgM and IgG assays combined could reduce the number of samples sent to the reference laboratory and thus reduce the time taken to obtain a final result.