Rheumatoid arthritis significantly increases the risk of potentially fatal blood clots in the legs and lungs, reveals a large nationwide study published online in the Annals of the Rheumatic Diseases.
Between 11% and 30% of people who develop a blood clot in the legs, known as a deep vein thrombosis or DVT, or a blood clot in the lungs, known as a pulmonary embolism, or PE, die within 30 days of their diagnosis, the evidence suggests.
Several studies have shown that chronic inflammation, which typifies rheumatoid arthritis, is linked to a heightened risk of thickened blood, but rheumatoid arthritis is not generally thought of as a risk factor for DVT or PE, say the researchers.
They therefore tracked the health of most of the population of Taiwan (23.74 million people) through the country's compulsory national insurance scheme between 1998 to 2008, and included a further monitoring period up to the end of 2010, to find out if rheumatoid arthritis increased the risk of potentially fatal blood clots.
Just fewer than 30,000 people developed rheumatoid arthritis during this period, and their details were entered into a national (catastrophic illness) registry of the National Health Insurance Database (NHIRD). By way of comparison, they were matched with almost 117,000 healthy people of the same age and sex.
Three quarters (77%) of those who developed rheumatoid arthritis were women, and the average age at diagnosis was 52. Around one in five were over the age of 65.
Patients with rheumatoid arthritis were more likely to have other underlying conditions, such as high blood pressure, diabetes, high cholesterol, heart failure and fractures, than were those in the comparison group.
But even after taking account of these influential factors, and allowing for age, patients with rheumatoid arthritis were still significantly more likely to develop potentially fatal blood clots, the analysis revealed.
They were more than three times as likely to develop a DVT, and twice as likely to develop a PE as those without the condition, the figures showed.
Furthermore, rheumatoid arthritis packed the greatest punch in the under 50s, who were almost six times as likely to develop a DVT and more than three times as likely to develop PE than were either middle aged (50 to 65) or older adults.
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