Clinical advantages from measurement of IgM-rheumatoid factor by enzyme immunoassay

Two enzyme immunoassays for rheumatoid factor (RF) were compared with the traditional latex agglutination test. Preference is expressed for an ELISA specific for IgM-RF because it yields specific, quantitative results. Variability of this assay was least in sera containing moderate levels of RF and it was less precise at low concentrations. Survey of a random selection from the local population showed a similar prevalence of IgM-RF positivity as revealed by previous surveys using agglutination techniques. We conclude that measurement by ELISA yields no great increase in the discriminative ability of RF testing.