title: Combined elevation of IgM and IgA rheumatoid factor has high diagnostic specificity for rheumatoid arthritis.
abstract: The diagnostic value of measuring rheumatoid factor (RF) by agglutination or isotype-specific enzyme-linked immunosorbent assay (ELISA) was compared. The study included 70 patients with rheumatoid arthritis (RA) and 205 patients with various other rheumatic conditions. Of the RA patients, 74% were RF-positive by agglutination and 90% had one or more RF isotypes elevated by ELISA compared to 14% and 22%, respectively, of the other patients. Strikingly, 70% of the RF-positive RA patients had an elevation of two or more RF isotypes compared to only 16% of the other RF-positive patients (P < 0.0001). Furthermore, a combined elevation of IgM and IgA RF was found in 52% of the RF-positive RA patients, but only in two (4%) of the other RF-positive patients (P < 0.0001). It is concluded that a combined elevation of IgM and IgA RF is highly specific for RA and is very rarely found in rheumatic diseases other than RA. Isotype-specific RF assays are therefore diagnostically superior to agglutination tests. The detection of the RA-specific RF isotype pattern may be particularly helpful early in the course of RA even before the disease is fully differentiated.
authors.affiliation: Department of Immunology, National University Hospital, Reykjavik, Iceland.
authors.forename: T
authors.initials: T
authors.lastname: Jónsson
authors.forename: K
authors.initials: K
authors.lastname: Steinsson
authors.forename: H
authors.initials: H
authors.lastname: Jónsson
authors.forename: A J
authors.initials: AJ
authors.lastname: Geirsson
authors.forename: J
authors.initials: J
authors.lastname: Thorsteinsson
authors.forename: H
authors.initials: H
authors.lastname: Valdimarsson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000372:Agglutination Tests; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis*; D007075:Immunoglobulin M / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000032:analysis*; D012680:Sensitivity and Specificity
chemical_list: D007070:Immunoglobulin A; D007075:Immunoglobulin M; D012217:Rheumatoid Factor