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Medline ® Abstract for Reference 90

of 'Epidemiology of, risk factors for, and possible causes of rheumatoid arthritis'

Elevated rheumatoid factor and long term risk of rheumatoid arthritis: a prospective cohort study.
Nielsen SF, Bojesen SE, Schnohr P, Nordestgaard BG
BMJ. 2012;345:e5244. Epub 2012 Sep 6.
OBJECTIVE: To test whether elevated concentration of rheumatoid factor is associated with long term development of rheumatoid arthritis.
DESIGN: A prospective cohort study, the Copenhagen City Heart Study. Blood was drawn in 1981-83, and participants were followed until 10 August 2010.
SETTING: Copenhagen general population.
PARTICIPANTS: 9712 white Danish individuals from the general population aged 20-100 years without rheumatoid arthritis at study entry.
MAIN OUTCOME MEASURES: Rheumatoid arthritis according to baseline plasma IgM rheumatoid factor level categories of 25-50, 50.1-100, and>100, versus<25 IU/mL.
RESULTS: Rheumatoid factor levels were similar from age 20 to 100 years. During 187,659 person years, 183 individuals developed rheumatoid arthritis. In healthy individuals, a doubling in levels of rheumatoid factor was associated with a 3.3-fold (95% confidence interval 2.7 to 4.0) increased risk of developing rheumatoid arthritis, with a similar trend for most other autoimmune rheumatic diseases. The cumulative incidence of rheumatoid arthritis increased with increasing rheumatoid factor category (P(trend)<0.0001). Multivariable adjusted hazard ratios for rheumatoid arthritis were 3.6 (95% confidence interval 1.7 to 7.3) for rheumatoid factor levels of 25-50 IU/mL, 6.0 (3.4 to 10) for 50.1-100 IU/mL, and 26 (15 to 46) for>100 IU/mL, compared with<25 IU/mL (P(trend)<0.0001). The highest absolute 10 year risk of rheumatoid arthritis of 32% was observed in 50-69 years old women who smoked with rheumatoid factor levels>100 IU/mL.
CONCLUSION: Individuals in the general population with elevated rheumatoid factor have up to 26-fold greater long term risk of rheumatoid arthritis, and up to 32% 10 year absolute risk of rheumatoid arthritis. These novel findings may lead to revision of guidelines for early referral to a rheumatologist and early arthritis clinics based on rheumatoid factor testing.
Department of Clinical Biochemistry, 54M1, Herlev Hospital, Copenhagen University Hospital, Herlev Ringvej 75, DK-2730 Herlev, Denmark.