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Elevated rheumatoid factor levels increased long-term risk for RA
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Healthy individuals with elevated plasma levels of the antibody rheumatoid factor had up to a 26-fold greater long-term risk for developing rheumatoid arthritis than those with normal levels in a prospective study.
Researchers in Denmark measured baseline plasma levels of IgM rheumatoid factor in 9,712 white Danish participants (52% women), aged 20 to 100 years, without diagnoses of rheumatoid arthritis (RA). The cohort, part of the Copenhagen City Heart Study, was divided into groups: participants with elevated rheumatoid factor levels of 25 to 50 IU/mL (n=176), 50.1 to 100 IU/mL (n=187), and greater than 100 IU/mL (n=55). They were compared with participants with normal levels of less than 25 IU/mL (n=9,294).
In a 28-year follow-up from 1981 to August 2010, 183 participants developed RA during 187,654 person-years. Researchers found that a doubling of rheumatoid factor level resulted in a statistically significant, multivariable-adjusted HR of 3.3 for developing RA (95% CI, 2.7-4.0). Risk for other autoimmune rheumatic diseases, including Sjögren’s syndrome (HR=1.8; 95% CI, 0.8-4.1), systemic lupus erythematosus (HR=2.5; 95% CI, 0.9-6.6) and systemic sclerosis (HR=3.1; 95% CI, 1.0-9.3), also showed similar trends that reached near significance.
Participants with rheumatoid factor levels of greater than 100 IU/mL were associated with a 26-fold increased risk for developing RA (HR=26; 95% CI, 15-46) compared with those with normal levels. Researchers said the highest absolute 10-year risk for RA was 32% and occurred in women aged 50 to 69 years who ever smoked and had rheumatoid factor levels greater than 100 IU/mL.
Although their study did not prove a causal relationship between rheumatoid factor levels and the pathogenesis of RA development, researchers concluded, “these novel findings may lead to revision of guidelines for early referral to a rheumatologist and early arthritis clinics based on rheumatoid factor testing.”
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