Researchers in Denmark have found that individuals with raised levels of an antibody known as rheumatoid factor in their blood have up to a 26-fold greater long term risk of developing rheumatoid arthritis (RA). The study, just published on bmj.com, indicates that even those people without typical arthritic symptoms like pain and swelling in the joints should get an early referral for examination after a positive rheumatoid factor test.
26-Fold Risk of RA!
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The team measured rheumatoid factor levels in 9, 712 Danish individuals aged 20 to 100 years without RA at the start of the study and followed them for up to 28 years. Raised rheumatoid factor levels of 25-50 IU/mL, 50.1-100 IU/mL and more than 100 IU/mL were compared with normal levels (less than 25 IU/mL). During the study period, 183 individuals developed rheumatoid arthritis.
After taking account of several other possible risk factors, a doubling of rheumatoid factor level was associated with a 3.3-fold increased risk of developing rheumatoid arthritis. The highest rheumatoid factor level (100 IU/mL or more) was associated with a 26-fold increased risk of developing the condition.
In the September 6, 2012 news release the authors stress that their study cannot prove that rheumatoid factor plays a causal role in the development of rheumatoid arthritis, but they conclude that the findings “may lead to revision of guidelines for early referral to a rheumatologist and early arthritis clinics based on a positive rheumatoid factor test – even in the absence of the typical arthritic joint symptoms.”
Dr. Nordestgaard told OTW,
If a patient without a diagnosis of rheumatoid arthritis is found to have elevated rheumatoid factor, he/she should be referred to a rheumatologist and early arthritis clinic. This is because a rheumatoid factor level above 100 versus below 25 IU/mL is associated with a 26-fold increased risk of developing rheumatoid arthritis, and because early treatment may prevent the disease from getting into the very severe stages. The highest risk was found in women who smoked and had a rheumatoid factor level above 100 IU/mL, where 1 in 3 women will develop rheumatoid arthritis over 10 years.
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This is a fascinating development. In my practice we've seen similar outcomes with the revised protocol. The key differentiator seems to be patient selection criteria. Has anyone else noticed the correlation with BMI thresholds?
Great point. I'd push back slightly on the conclusion, the sample size in the cited study is too small to draw population-level inferences. That said, the directional signal is compelling and worth a larger RCT.
We implemented a similar approach last year. Early results are promising but we're still gathering 12-month follow-up data. Happy to share our protocol if anyone is interested.
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