title: Clinical significance of rheumatoid factor isotypes in seropositive arthritis.
abstract: In this cross-sectional study a comparison was made of rheumatoid factor (RF) isotypes in 203 RF positive patients with arthritis. Of these, 129 had rheumatoid arthritis (RA) and 74 a milder disease that would formerly have been classified as probable RA. The majority (74%) of the RA patients had elevations of two or three RF isotypes compared with only 34% of the patients with the milder form of arthritis. A striking feature was that combined elevation of IgM RF and IgA RF was found in 67% of the RA patients compared to only 20% of the patients with milder arthritis who most frequently had an isolated elevation of IgM RF (41%). RA patients with an isolated elevation of IgA RF were younger and had a shorter disease history than RA patients with an isolated elevation in IgM RF or a combined elevation of IgA RF and IgM RF. The prevalence of raised IgM RF was, furthermore, found to increase with age and disease duration. We conclude that a raised level of IgA RF is an adverse phenomenon in patients with seropositive arthritis while patients with an isolated increase in IgM RF may be expected to experience a relatively mild disease course.
authors.affiliation: Department of Immunology, National University Hospital, Reykjavík, Iceland.
authors.forename: T
authors.initials: T
authors.lastname: Jónsson
authors.forename: H
authors.initials: H
authors.lastname: Valdimarsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000453:epidemiology / Q000276:immunology*; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis; D007132:Immunoglobulin Isotypes / Q000032:analysis*; D007075:Immunoglobulin M / Q000032:analysis; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000032:analysis* / Q000276:immunology; D012720:Severity of Illness Index; D013997:Time Factors
chemical_list: D007070:Immunoglobulin A; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D012217:Rheumatoid Factor