(RxWiki News) To give a solid diagnosis of rheumatoid arthritis, doctors look for a number of signs, including evidence from blood tests. Can these blood tests also show arthritis risk in people who are arthritis-free?
Researchers found that higher levels of a protein called rheumatoid factor may predict the long-term risk of rheumatoid arthritis in people without the condition.
In a recent study, people with higher levels of rheumatoid factor were more likely to develop rheumatoid arthritis than those with normal levels.
"Seek arthritis treatment early."
Research has shown that early treatment of rheumatoid arthritis with disease-modifying antirheumatic drugs (DMARDs) can put the disease into remission (lessening of symptoms).
Unfortunately, doctors have few tools for identifying people's long-term risk of rheumatoid arthritis, said Professor Børge Nordestgaard of the University of Copenhagen and colleagues in the introduction of their study.
Even though no blood test can absolutely diagnose rheumatoid arthritis, the presence of rheumatoid factor is a sign of the condition. However, researchers are not sure if high levels of the protein in people without rheumatoid arthritis are a sign that they will develop the condition in the future.
Professor Nordestgaard and colleagues found that raised levels of rheumatoid factor were associated with the long-term development of rheumatoid arthritis.
People who had a doubling of rheumatoid factor had a 3.3-fold increased risk of developing rheumatoid arthritis within 28 years.
People with the highest levels of rheumatoid factor (100 IU/mL or more) had a 26-fold increased risk of rheumatoid arthritis within 28 years.
Even though this represents a large increased risk, the absolute risk of rheumatoid arthritis remains low (about 1 percent in the general population). In the study, the 26-fold increased risk affected a very small number of patients.
It is important to keep in mind, though, that only 40 percent of rheumatoid arthritis patients test positive for rheumatoid factor at the onset of their disease, the authors said. That is, rheumatoid factor is not a definite sign of rheumatoid arthritis.
Furthermore, rheumatoid factor is a minor part of the diagnosis of rheumatoid arthritis. To be diagnosed with rheumatoid arthritis, patients must have at least one joint with synovitis (inflammation) and no other diagnosis that could explain the synovitis. Patients also must show evidence of arthritis in a number of ways, including evidence from blood tests, number of affected joints and duration of symptoms.
Results of the study also showed that older women (50 to 69 years of age) with the highest levels of rheumatoid factor and who smoked had a 32 percent absolute risk of developing rheumatoid arthritis within 10 years.
The authors said that this finding is yet another reason for people to quit smoking.
The study involved 9,712 white Danish people between 20 and 100 years of age. None of the participants had rheumatoid arthritis at the beginning of the study. The researchers compared arthritis rates in people with normal levels of rheumatoid factor (less than 25 IU/mL) to rates in those with raised levels (25-50 IU/mL, 50.1-100 IU/mL and 100 IU/mL or more). By the end of the study, 183 participants developed rheumatoid arthritis.
The research was funded by Herlev Hospital, Copenhagen University Hospital and the Danish Heart Foundation.
The study was published September 6 in BMJ.