High predictive value of Toxoplasma gondii IgG antibody levels in HIV-infected patients for diagnosis of cerebral toxoplasmosis.

The results of serological tests for Toxoplasma gondii IgG in 31 HIV-infected patients with toxoplasmic encephalitis (TE) and 49 HIV-infected patients seropositive for Toxoplasma gondii but without TE were compared. All patient had a CD4+ lymphocyte count < 150/microliters. Of the TE patients, 22 (71%) were designated as having relatively high IgG levels on the basis of the following Toxoplasma IgG titre combination: Sabin-Feldman test > or = 1:256, indirect hemagglutination test > or =1:1024, direct agglutination test > or = 1:14,580. Only 3 patients without TE had relatively high IgG titres. Relatively high IgG titres indicated TE with a positive predictive value of 88% in HIV-infected patients with CD4+ cell counts < 150/microliters, and could be observed in most patients several months prior to the first clinical and radiological signs of TE.