Comparison of two immunoassay procedures for detecting enterovirus IgM.

Enteroviruses cause significant illness in man but viral diagnosis is problematic. Enterovirus-specific IgM tests have been developed but due to the difficulties of obtaining reliable control sera the interpretation of assay data remains mainly arbitrary and empirical. The present study was undertaken to assess the reliability of such assays by comparing two tests performed independently in two different laboratories: a mu-capture radioimmunoassay (MACRIA) which utilizes 35S-labelled Coxsackie virus antigens and an enzyme immunoassay (EIA). A feature of the MACRIA was that sera were tested in one large batch whereas the EIA was in routine use in a reference laboratory. The MACRIA was easy to perform but more suitable for research investigations than routine diagnostic use. Similar results were detected in the majority of sera tested in the two assays with 85% concordance achieved on testing 120 sera. Of the 18 discrepant results, 11 were positive by EIA only and 7 by MACRIA only. 89-95% concordance was obtained on testing sera against individual Coxsackie B1-5 serotypes, moreover 52% of the sera positive in MACRIA were reactive against only one viral antigen and the results on certain of the more strongly reactive sera suggested the existence of a measure of type specificity in the MACRIA test. Qualitative differences between the two tests highlighted problems of interpretation in the absence of a gold standard and cautioned against sole reliance on serology for diagnosis of enteroviral infections.