Contribution of the "Recomline Toxoplasma IgM" Kit in the Distinction between Toxoplasmic IgM and Natural IgM

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Diagnosis of toxoplasmosis is based essentially on serology by systematically searching for anti-toxoplasmic IgG and IgM. One of the difficulties encountered in the interpretation of Toxoplasma serology in pregnant women is the distinction between anti-Toxoplasma IgM and non-specific IgM called "natural". A total of 58 sera from pregnant women have been tested. All these sera were positive in ELISA-IgM and negative in ELISA-IgG and IFI-IgG. These sera are divided into 2 groups: Group 1: 30 sera with natural IgM confirmed after 3 weeks checkups for a period up to 3 months. Group 2: 28 sera with specific anti-toxoplasmic IgM. The 28 sera were tested by the immunoblot kit using the recomLine Toxoplasma IgM assay.  This test is based on 8 recombinant toxoplasmic antigens which are: ROP1c, MIC3, GRA7, GRA8, p30, MAG1, GRA1, and rSAG1. Among the 28 confirmed IgM-specific sera, 11 sera were positive in recomLine Toxoplasma IgM, that is, a sensitivity of 39.3% [22.1-59.3]. Among the 30 confirmed natural IgM sera, 28 sera were negative in recomLine Toxoplasma IgM, that is, a specificity of 93.33% [76.5-98.8]. Positive predictive value and negative predictive value were 84.6% [53.7-97.3] and 62.2% [46.5-75.8], respectively. In conclusion, the recomLine Toxoplasma IgM test can be recommended in situations where IgM is positive and IgG is negative. The positivity of this test makes the diagnosis of toxoplasma seroconversion very likely. However, its negativity does not rule out the diagnosis.