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 patients had a CD4+ lymphocyte count < 150/mu l. 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 greater than or equal to 1:256, indirect hemagglutination test greater than or equal to 1:1024, direct agglutination test greater than or equal to 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/mu l, and could be observed in most patients several months prior to the first clinical and radiological signs of TE.