CURRENT STRATEGIES IN THE LABORATORY DIAG NOSIS OF OCULAR TOXOPLASMOSIS

Background The diagnosis of ocular toxoplasmosis has remained a merely clinical one, because the low sensitivity of established methods does not allow clinical consequences. The underlying open prospective stud y was undertaken to analyse the sensitivity of a combination including the newly available tests for the diagnosis of the disease. Methods F rom 27 patients included until now, aqueous humor and serum samples we re collected and sent to one of two reference laboratories according t o their actual availability. From all samples, total IgG and anti-Toxo plasma IgG as well as specific IgM and IgA were quantified, and from t he results, the antibody ratio was calculated according to the formula of Goldmann and Witmer. From the samples sent to laboratory 2, antibo dy avidity was determined and Toxoplasma DNA amplified using PCR. Resu lts A confirmation of the clinical diagnosis was achieved in 5/9 cases (56%) from samples sent to laboratory 1, and from 14/18 samples (78%) sent to laboratory 2. Calculation of the antibody ratio was confirmed to be the most sensitive method with a confirmation rate of 41%, foll owed by PCR (28%), determination of specific IgA (22%) and finally ant ibody avidity (15%). A confirmation with two independent tests was ach ieved in 28% of cases. Conclusion None of the methods analysed was sen sitive enough to establish the diagnosis in a given case. The combinat ion of all four methods, however, achieved a sensitivity, which is hig h enough to justify a clinical routine analysis of aqueous humor sampl es.