And, it’s important to note, that the vast majority of RA study subjects did not suffer a blood clot during the study follow-up period. “Less than 3 percent of the RA patients had a blood clot,” Dr. Holmqvist says. “This is not extremely high, but comparable to the absolute risk of myocardial infarction [heart attack] that we and many others have reported previously.”

Still, Dr. Holmqvist suggests it’s a health situation that bears watching. “It might be that we need to start thinking about taking preventive measures to decrease the risk of this comorbidity. How [to do that] is trickier, since we know less about what is causing the increased risk,” she says.

Dr. Holmqvist says there are several hypotheses. “We know that acute inflammation [affects] coagulation factors that could be of importance in the formation of clots,” she explains. “We also know that RA patients smoke to a higher extent than the general population and that smoking is a risk factor for clots.”

Another risk factor, she says, is the fact RA patients generally have less mobility than their healthy counterparts. “So far, we don’t know. And one important future challenge is to find out why and how we can prevent it,” she adds.

So, what should an RA patient do with this information?

“I don’t think that patients with rheumatoid arthritis should be overly alarmed,” says Jack Ansell, MD, professor of medicine at New York University School of Medicine and Chair of the Department of Medicine at Lenox Hill Hospital, New York, N.Y. “The risk factor is still relatively low. But it’s important to know. And patients might want to ask their doctor, if they are hospitalized and have rheumatoid arthritis, whether they are at risk of developing blood clots.”

Dr. Ansell says the Swedish study is a good opportunity to focus on a deadly health problem many are not aware of: “Six hundred thousand people a year in the United States develop VTE,” he says. The Centers for Disease Control and Prevention reports that as many as 60,000 to 100,000 die annually of it.

“VTE is often a complication of another disease. So when somebody has cancer and they die of cancer, the fact is they may have died of a pulmonary embolism (blood clot in the lung) because blood clots are a major risk factor of cancer,” Dr. Ansell adds. “It’s important to get the message out that VTE is a medical problem people should be aware of,” he says.