Lupus patients are four times more likely than people without an autoimmune disease to develop blood clots when hospitalized. Rheumatoid arthritis, or RA, patients are one-and-a-half times more likely to develop blood clots during a hospital stay, and anyone with an immune-related disorder faces some sort of increased risk, according to a new study from researchers in the United Kingdom.

“For some diseases, such as RA, the risk increase is fairly small in epidemiological terms, but for others the effect is much greater. For example, systemic lupus erythematosus has nearly a four-fold risk increase,” says Sreeram Ramagopalan, PhD, a study author from the University of Oxford in the United Kingdom. “These blood clots are potentially fatal and this data should be taken into account when patients with autoimmune disease are admitted to the hospital so that preventative measures can be taken.”

Ramagopalan says it was previously known that patients with some autoimmune diseases, like Crohn’s disease and type 1 diabetes, had an increased risk of blood clots. But he says this study, published online in the journal BMC Medicine, shows for the first time that patients with many other autoimmune diseases have this increased risk as well.

To determine that risk, researchers at the University of Oxford reviewed 45 years of medical records in England, looking for signs of a blood clot in the veins (known as venous thromboembolism or VTE) of patients hospitalized for immune-related disorders and for non-immune related reasons.

Researchers discovered that polyarteritis nodosa, a disease of the blood vessels, increases risk 3.5 times. Like lupus, researchers categorize this as high risk. People with psoriasis are 1.6 times more likely to develop blood clots, and people with ankylosing spondylitis, a disease characterized by inflammation of the spine, are 1.9 times more likely.

“The increased risk for blood clots is for when hospitalized in general, and even when not hospitalized. We showed that patients being admitted to the hospital for an autoimmune disease episode had an increased risk for VTE more than 90 days after the admission for the autoimmune disease,” Ramagopalan says. “For example, patients were readmitted to the hospital for VTE months after coming in for their autoimmune disease episode.”

Researchers say it’s possible that inflammation is causing this increased risk. “It needs to be studied as to exactly why patients with autoimmune disease are at an increased risk, but there is good evidence to suggest that autoimmune processes may lead to clots,” Ramagopalan says.

Michael Streiff, MD, medical director of the Anticoagulation Management Service and Outpatient Clinics at Johns Hopkins Medical Institutions in Baltimore says the study is part of a growing body of literature supporting a connection between inflammation and VTEs.

“Inflammation is associated with changes in the blood that tip the hemostatic balance toward clot formation. These findings are consistent with previous studies demonstrating an increased risk of blood clots in patients with inflammatory bowel disease and infections,” Dr. Streiff says. “It makes sense biologically that these patients would be at higher risk for blood clots.”

Given their findings, study researchers suggest patients at increased risk of blood clots consider asking for and taking anti-clotting drugs while they’re in the hospital. “It has been estimated that there are thousands of deaths in hospitals due to VTE, which could have potentially been prevented,” Ramagopalan says.

Dr. Streiff agrees. “[Patients] need to say, ‘I hear I’m at higher risk because I have RA and am in the hospital,’ and make sure their doctors are giving them that medicine,” Dr. Streiff says. He says patients may need to continue taking the medication when they check out too, particularly if they are in the hospital for only a few days.

“Often times we just give those [medications] for the duration of the hospitalization, but the risk of blood clots often extends beyond a few day hospital stay, as many patients are still recovering from an illness after they return home. Perhaps some rheumatologic conditions, such as lupus, warrant continued treatment with anti-clotting drugs after discharge,” Dr. Streiff explains. “Further studies of the risk of clotting posed by these illnesses and the preventive benefits of anti-clotting medications are warranted.”