[Current limits in diagnosis of ocular toxoplasmosis]

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 study was undertaken to analyse the sensitivity of a combination including the newly available tests for the diagnosis of the disease.

From 27 patients included until now, aqueous humor and serum samples were collected and sent to one of two reference laboratories according to their actual availability. From all samples, total IgG and anti-Toxoplasma IgG as well as specific IgM and IgA were quantified, and from the results, the antibody ratio was calculated according to the formula of Goldmann and Witmer. From the samples sent to laboratory 2, antibody avidity was determined and Toxoplasma DNA amplified using PCR.

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%, followed by PCR (28%), determination of specific IgA (22%) and finally antibody avidity (15%). A confirmation with two independent tests was achieved in 28% of cases.

None of the methods analysed was sensitive enough to establish the diagnosis in a given case. The combination of all four methods, however, achieved a sensitivity, which is high enough to justify a clinical routine analysis of aqueous humor samples.