Plasma biomarker predicts rheumatoid arthritis onset

By Lynda Williams, Senior medwireNews Reporter

Healthy individuals with high levels of immunoglobulin G rheumatoid factor have a significantly increased risk for developing rheumatoid arthritis (RA), suggests population-based research published in the BMJ.

Individuals with a rheumatoid factor level above 100 IU/mL were 26 times more likely to develop RA over 20 years than those with levels below 25 IU/mL, after adjusting for confounding factors such as age, smoking, and body mass index.

Increased risks for RA were also found for individuals with lower levels of rheumatoid factor, with significant hazard ratios of 3.6 for 25-50 IU/mL and 6.0 for 50.1-100 IU/mL, report Børge G Nordestgaard and co-workers from Herlev Hospital in Denmark.

Rheumatoid factor plasma levels were measured in 9712 White Danish healthy citizens aged 20-100 years old in 1981 to 1983, and the participants were followed up until 2010. Over 187,659 person-years of follow up, 183 participants were diagnosed with RA.

The 10-year absolute risk for RA varied with age, gender, and smoking habits, peaking at 32% in female smokers aged 50-69 years with a rheumatoid factor level above 100 IU/mL. Men aged over 70 years old with a rheumatoid factor level below 25 IU/mL had the lowest 10-year risk, at 0.1%, and smoking status did not influence risk in this group.

"Our finding of high risks of developing [RA] based on elevated levels of rheumatoid factor alone suggests the need for early referral to a rheumatologist or to early arthritis clinics for examination on the basis of a positive rheumatoid factor test - even in the absence of the typical arthritic joint symptoms - because of the better response to therapy the earlier it is initiated in rheumatoid arthritis," they say.

However, Julia Simard and Marie Holmqvist, from Karolinska Institutet in Stockholm, Sweden, say in an accompanying commentary that "rheumatoid factor testing tends to follow a clinical suspicion so it is unclear how often such incidental findings are likely to occur in clinical practice. The authors do not explicitly suggest screening, so individuals are likely to be detected as seropositive only rarely."

Noting that anticitrullinated protein antibody is more specific and more widely used for RA diagnosis now than rheumatoid factor, they suggest further research should investigate the ability of this autoantibody to predict RA development.

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