Interference by Rheumatoid Factor in Immunoglobulin M-Class Herpes Simplex Virus Types 1 + 2 Immunoassays

Herpes simplex virus (HSV) types 1 + 2 immunoglobulin (Ig)M antibodies assays are important tools for diagnosing pregnant women and their newborns. However, it is unclear whether high levels of rheumatoid factor (RF) interfere with serological methods used to test for HSV types 1 + 2 type-specific IgM antibodies. We report a case of a false-positive result for HSV 1 + 2 IgM antibodies due to gross overestimation of RF by enzyme-linked immunosorbent assay (ELISA). This result occurred in a 25-year-old Han Chinese woman who was 28 weeks pregnant with a fetus (sex of fetus unknown). Antinuclear antibody (ANA) screening was performed, and RF-absorbent material was used. Test results for 3 antibodies of ANA (SSA, Ro-52, and SSB) were positive; the rest of the results were negative. Also, RF levels were significantly higher than normal, as measured by ANA screening. We observed an obvious decrease in HSV 1 + 2 IgM antibodies after removal of RF. Based on our findings, the presence of high concentrations of RF may be responsible for false-positive HSV 1 + 2 ELISA results.