Serologic Diagnosis of Toxoplasmosis with Emphasis on the Detection of Toxoplasma-specific Immunoglobulin M Antibodies

Abstract
Commercially available kits were used for the detection of Toxoplasma-specific IgM antibodies. False positive IgM results were observed in whole sera containing Toxoplasma-specific antibodies together with rheumatoid factor when tested by immunofluorescence (IFA). False negative IgM results occurred in whole sera containing competing levels of Toxoplasma- specific IgG antibodies, as indicated by the IFA:IgM-M ratio. False positive and false negative IgM results often occurred when whole sera were tested. These false reactions were eliminated by fractioning IgM from IgG using the Isolab’s IgM Isolation System®. All five sera in this study with an IFA titer to Toxoplasma of ≥1:16,384 also contained Toxoplasma-specific IgM antibodies. This suggests that sera with high titers to Toxoplasma should be tested for Toxoplasma-specific IgM antibodies.

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