FRIDAY, Sept. 7 (HealthDay News) — Elevated blood levels of an antibody called rheumatoid factor are associated with an increased long-term risk of rheumatoid arthritis, a new study contends.
Women in their 50s and 60s who smoke appear to have the highest risk, according to the Danish researchers.
The researchers measured rheumatoid factor levels in more than 9,700 people, aged 20 to 100, who did not have rheumatoid arthritis at the start of the study. The participants were followed for up to 28 years. During that time, 183 people developed rheumatoid arthritis.
People with a rheumatoid factor level twice the normal level (less than 25 international units per milliliter) had a 3.3-fold increased risk of developing rheumatoid arthritis. Those with the highest rheumatoid factor levels (100 IU/mL or more) had a 26-fold increased risk.
The highest 10-year risk of rheumatoid arthritis (32 percent) was found in women aged 50 to 69 who smoked and had rheumatoid factor at the highest levels. The lowest 10-year risk (0.1 percent) was found in men 70 and older with rheumatoid factor at normal levels.
The findings do not prove that rheumatoid factor is a cause of rheumatoid arthritis, but do suggest that people with a positive rheumatoid factor test should be referred to a rheumatologist for examination, the researchers said.
The study was published online Sept. 6 in the British Medical Journal.
Rheumatoid arthritis is a chronic inflammatory joint disorder that affects about 1 percent of people worldwide, according to the American College of Rheumatology. Women are three times more likely to develop the condition than men.
More information
The American Academy of Family Physicians has more about rheumatoid arthritis.