Assessment of the specificity of a commercial human parvovirus B19 IgM assay

Background: It is important to investigate a possible cross-reaction of anti-rubella IgM in the IDEIA^™ Parvovirus B19 IgM test because many B19 infections are either asymptomatic or have clinical symptoms similar to those of rubella virus infections. Epstein-Barr virus (EBV) IgM, cytomegalovirus (CMV) IgM, measles IgM and rheumatoid factor (RF) IgM cross-reactions were also studied.

Objectives: In the period from February to September 1994 (including a parvovirus B19 epidemic) more than 10 000 serum samples were examined for parvovirus B19 IgM in Denmark. This gave an opportunity to evaluate the commercial IDEIA^™ Parvovirus B19 ELISA kit (DAKO A/S, Glostrup, Denmark), which was used routinely at Statens Serum Institut from the beginning of 1994 and onwards.

Study design: A total of 123 parvovirus B19 IgM positive sera were tested for reactivity in rubella IgM EIA. A total of 78 rubella IgM positive sera, 60 EBV VCA-IgM positive sera, 30 CMV IgM positive sera and 24 measles virus IgM positive sera were tested for reaction in IDEIA^™ Parvovirus B19 IgM test. Finally, 25 parvovirus IgM positive sera were tested for specific IgM against measles virus, EBV (VCA), CMV and for RF.

Results: One anti-B19 IgM positive serum sample reacted positively in the rubella IgM test. Of rubella IgM positive serum samples 4% cross-reacted in IDEIA^™ Parvovirus B19 IgM test, as did 17 and 20% of EBV VCA-IgM and CMV IgM positive serum samples respectively. None of measles virus IgM positive serum samples cross-reacted in the IDEIA^™ Parvovirus B19 IgM test. Of 25 initially parvovirus B19 IgM positive sera 20% cross-reacted in EBV VCA IgM test and 8% in the CMV IgM test. None reacted positively in measles virus IgM test; 28% showed weak reactivity in RF IgM test.

Conclusions: Precautions must be taken when results of IgM assays are interpreted. Epidemiological and clinical observations must be considered.