People with elevated levels of an antibody called rheumatoid factor appear to have a significantly increased risk of developing rheumatoid arthritis in the long term, scientists say, reports Arthritis Research UK.
Researchers at the University of Copenhagen in Denmark measured the levels of rheumatoid factor in blood samples from 9,712 people, aged 20 to 100 years – all of whom were free of rheumatoid arthritis at the start of the study.
Participants were then followed for up to 28 years to see whether they developed the autoimmune disease.
A total of 183 people developed rheumatoid arthritis during the follow-up period.
The researchers discovered that men and women who had elevated levels of rheumatoid factor at the start of the study were more likely to develop the disease.
After other risk factors had been taken into account, a doubling in a person’s levels of rheumatoid factor was found to be associated with a 3.3-fold increased risk of developing rheumatoid arthritis.
Those with the highest levels (100 IU/mL or more, compared with a normal level of less than 25 IU/mL) faced a 26-fold increase in their risk of the disease.
The study authors also observed that female smokers in their 50s or 60s who had rheumatoid factor levels of 100 IU/mL or more seemed to face the most significant risk.
Writing in the British Medical Journal, the study authors argued that their finding “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”.
Professor Alan Silman, medical director of Arthritis Research UK, commented: “This research is interesting in confirming the effectiveness of the rheumatoid factor test in signalling the increased long-term risk of developing rheumatoid arthritis. However it’s not new, and it’s been known for many years that many people who have rheumatoid factor don’t develop rheumatoid arthritis, and that in others rheumatoid factor can be present in their blood for 20 years before it does develop.
“Using the rheumatoid factor test as a screening device could create unnecessary anxiety, and would also of limited practical or clinical use as it would mean offering a blood test to people without any symptoms of rheumatoid arthritis.
“Other tests are usually also carried out to confirm the diagnosis, such as another antibody test known as anti-CCP. People with the signs and symptoms of rheumatoid arthritis who test positive for rheumatoid factor and another antibody test called anti-CCP are likely to have more severe rheumatoid arthritis.”