Diagnosis of congenital toxoplasmosis at birth: what is the value of testing for IgM and IgA?

Recommandations vary on the best combination of tests to use for the diagno sis of subclinical congenital toxoplasmosis at birth. The diagnostic accura cy of IgM and IgA tests was assessed in the context of routine clinical pra ctice on 233 newborns with congenital toxoplasmosis and 661 healthy control s. IgM/IgA sensibility and specificity were compared in cord and postnatal samples. Both tests were considerably more specific in neonatal blood (IgM: 98%; IgA: 100%) than in cordblood (IgM: 85%, IgA: 88%). Sensitivity for Ig M and IgA was not significantly different in neonatal blood (61% and 60%, r espectively) and cord blood (67% and 54%, respectively). Combining IgM and IgA increased the overall sensitivity to 73% without any significant loss i n specificity (98%). The influence of the date of maternal infection on the sensitivity and negative predictive value was also clearly demonstrated. Conclusion Because of their relatively low cost compared to more sophistica ted methods, IgM and IgA tests should remain the main method for the routin e diagnosis of congenital toxoplasmosis although follow up is essential to identify the Ca. 25% of infected children who are missed at birth on the ba sis of these tests.