Fluoroimmunoassay for detection of rubella-specific immunoglobulin M: comparison with indirect enzyme immunoassay and mu-chain capture.

The performance of a commercially-available method of fluoroimmunoassay (Rubella M FIAX, International Diagnostic Technology, Santa Clara, Calif.), designed for the detection of rubella-specific immunoglobulin M, was tested with 137 selected sera, including 52 from cases of primary rubella, 29 from healthy pregnant women, 21 containing rheumatoid factor, and 35 from cases of infectious mononucleosis (IM) caused by Epstein-Barr virus. The results were compared with those obtained by commercial indirect enzyme immunoassay (EIA) and EIA anti-mu chain capture tests. The fluoroimmunoassay technique showed a satisfactory level of sensitivity, but low values had to be interpreted with caution as false-positive results were detected with sera with rheumatoid factor and from IM cases, even after preliminary treatment of sera with the anti-human immunoglobulin G antisera provided in the kit. On the other hand, no false-positive results in the analysis of IM sera were seen in the EIA anti-mu chain capture method. Because of its sensitivity and specificity, we recommend the use of the latter technique for the diagnosis of primary rubella.