title: Elevated rheumatoid factor and long term risk of rheumatoid arthritis: a prospective cohort study.
abstract: OBJECTIVE
  To test whether elevated concentration of rheumatoid factor is associated with long term development of rheumatoid arthritis.
  
  
  METHODS
  A prospective cohort study, the Copenhagen City Heart Study. Blood was drawn in 1981-83, and participants were followed until 10 August 2010.
  
  
  METHODS
  Copenhagen general population.
  
  
  METHODS
  9712 white Danish individuals from the general population aged 20-100 years without rheumatoid arthritis at study entry.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Clinical Biochemistry, 54M1, Herlev Hospital, Copenhagen University Hospital, Herlev Ringvej 75, DK-2730 Herlev, Denmark.
authors.forename: Sune F
authors.initials: SF
authors.lastname: Nielsen
authors.forename: Stig E
authors.initials: SE
authors.lastname: Bojesen
authors.forename: Peter
authors.initials: P
authors.lastname: Schnohr
authors.forename: Børge G
authors.initials: BG
authors.lastname: Nordestgaard
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000209:etiology; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012372:ROC Curve; D012217:Rheumatoid Factor / Q000097:blood*; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects; D055815:Young Adult
chemical_list: D012217:Rheumatoid Factor