By Kathleen Doheny
People with this inflammatory form of arthritis are more than three times as likely to develop a deep vein thrombosis (a clot usually in the legs) and twice as likely to have a pulmonary thromboembolism (a clot that travels to the lungs) compared to those without the diagnosis, the new study found.
"I would call this a moderate increased risk," said Dr. Tore Kvien, editor-in-chief of the journal Annals of the Rheumatic Diseases and head of rheumatology at Diakonhjemmet Hospital in Oslo, Norway.
The research was published online Aug. 7 in the journal.
"This study is consistent with what our study and other published papers found," said Dr. Seoyoung Kim, assistant professor of medicine at Brigham and Women's Hospital and Harvard Medical School in Boston. In her study, Kim and her colleagues also reported an increased risk of blood clots in rheumatoid arthritis patients.
In the new study, the researchers used a national database to identify about 30,000 people who developed rheumatoid arthritis from 1998 to 2008. They monitored them through 2010 to see if the rheumatoid arthritis diagnosis affected blood clot risk.
Even after taking into account other health conditions such as high blood pressure, surgery and cancer, those with rheumatoid arthritis were still more likely to develop the blood clots than those not diagnosed with rheumatoid arthritis.
Patients younger than 50 were especially vulnerable, the researchers found.
About 1.3 million people in the United States -- about 0.4 percent of the population -- have rheumatoid arthritis, according to the Arthritis Foundation. In rheumatoid arthritis, the immune system attacks the body's own tissues, especially the thin membrane lining the joints. This results in chronic pain and inflammation. The cause is unknown, but experts believe genetic and environmental factors are involved.
Besides being aware of the link with clots, Kvien suggested that those with rheumatoid arthritis be as physically active as possible.
The researchers can't fully explain their findings, but it is thought that chronic inflammation plays a role.
The increased risk may be associated with inflammation, said Kim, or with the rheumatoid arthritis treatments.
Patients with rheumatoid arthritis who need surgery, cancer treatment or hospitalization should be placed on a clot-prevention regimen, she said. People with the disease also should try to live a healthy lifestyle to minimize the likelihood of clots.
"At this point, patients with RA should do their best to avoid modifiable risk factors for blood clots," said Dr. Diane Horowitz, a rheumatologist at North Shore University Hospital in Manhasset, N.Y., and Long Island Jewish Medical Center in New Hyde Park, N.Y. That means not smoking and avoiding prolonged periods of immobility, said Horowitz, who was not involved in the study.
Anyone with rheumatoid arthritis who has had a blood clot should discuss the new findings with their rheumatologist, Horowitz said.