Blood Tests Evaluated for Screening for Toxoplasmosis

Three blood serum tests have been evaluated of their potential as screening methods for the diagnosis of toxoplasmosis in pregnant women.

The assays were the classical Sabin–Feldman dye test (DT), an immunosorbent agglutination assay for immunoglobulin-M (ISAGA-IgM) and an automated electrochemiluminescence immunoassay (ECI) for both IgM and immunoglobulin-G (IgG).

Scientist at the Medical University of Vienna (Vienna, Austria), analyzed serum samples from 927 pregnant women, including 100 negative, 706 chronic, and 121 acute infections of Toxoplasma gondii.

The combination of the Elecsys Toxo IgG and IgM immunoassays (ECI) demonstrated high sensitivity and specificity of 97.1% and 100.0%, respectively, and a positive and negative predictive value of 100.0% and 81.3%, respectively.

The Elecsys Toxo IgG and IgM immunoassays (Roche Diagnostics, Mannheim, Germany) were found to be easy-to-use and fast test systems that provide results within 18 minutes, and therefore appropriate for high-throughput analysis in daily routine. The assay was designed to be used on Roche's "cobas e” immunoassay analyzers for the in vitro quantitative determination of IgG and IgM antibodies.

Untreated infection with the protozoan T. gondii during pregnancy can lead to fetal infection with serious consequences. T. gondii may cause a broad spectrum of clinical diseases, varying from subclinical infection to congenital toxoplasmosis with severe symptoms such as retinochoroiditis, intracerebral calcifications, hydrocephalus, and mental retardation. The transmission of the parasite occurs from the ingestion of insufficiently cooked meat or contact with cats.

The authors concluded that the Elecsys test system is appropriate for first-line serologic prenatal screening carried out within the first trimester and in seronegative pregnant women, and follow-up serology is recommended at eight-week intervals to identify seroconversions. However, for discrimination between chronic and acute infection, retesting by a reference laboratory should be mandatory to discriminate between pre- and postconceptional infection to start antiparasitic treatment to avoid mother-to-fetus transmission and severe sequelae. The study was published in December 2010, in Diagnostic Microbiology and Infectious Disease.

Related Links:
Medical University of Vienna
Roche Diagnostics