People with rheumatoid arthritis (RA) are at an increased risk of suffering a potentially fatal blood clot in their legs or lungs, a new study indicates.

RA is a chronic and often painful disease affecting the joints, causing them to become inflamed. An inflamed joint looks swollen and red and appears warm to touch. This inflammation can lead to permanent damage in the joints if the disease is not treated. Around 40,000 people in Ireland are affected.

Deep vein thrombosis (DVT) is a condition in which a blood clot forms within the deep vein system, often in the lower part of the body such as the legs. The main complication of DVT is pulmonary embolism (PE), which is the name given to a blood clot that lodges in one of the blood vessels that supplies the lungs with blood.

According to the researchers who carried out this study, between 11% and 30% of people who develop DVT or PE die within 30 days of the diagnosis. While studies have shown that chronic inflammation increases the risk of these conditions, until now, RA was not considered a risk factor for DVT or PE.

The researchers decided to investigate this further. They tracked the health of over 23 million people living in Taiwan - that is most of the population. This was done via an analysis of the country's national insurance scheme, which is compulsory.

The population was tracked from 1998 to 2010. During this period, almost 30,000 people were newly diagnosed with RA. These were then compared to 117,000 people without the condition.

Three in four people who developed RA were women. Their average age was 52.

The study found that those with RA were more likely to have other health conditions, such as diabetes, high cholesterol and high blood pressure, compared to those without RA.

However, even when these underlying conditions and the participants' age was taken into account, those with RA were still much more likely to develop dangerous blood clots. In fact, they were at least three times more likely to develop DVT and twice as likely to develop PE compared to their peers without RA.

This risk was even greater in younger people with RA. Those under the age of 50 with the joint condition were almost six times more likely to develop DVT and three times more likely to develop PE than those over the age of 50 with RA.

Details of these findings are published in the journal, Annals of the Rheumatic Diseases.

For more information on RA, see our RA Clinic here