The risk of pulmonary embolism and deep vein thrombosis in rheumatoid arthritis: a UK population-based outpatient cohort study

Background Recent hospital-based studies have suggested a sixfold increased risk of pulmonary embolism (PE) in rheumatoid arthritis (RA) in the year following admission. We evaluated the risk of PE and deep vein thrombosis (DVT) and associated time trend among RA patients (84.5% without a history of hospitalisation during the past year) derived from the general population. Methods We conducted a cohort study using an electronic medical records database representative of the UK general population, collected from 1986 to 2010. Primary definitions of the RA cohort (exposure) and PE/DVT outcomes required physician diagnoses followed by corresponding treatments. We estimated relative risks (RRs) of PE and DVT compared with a matched non-RA comparison cohort, adjusting for age, sex, smoking, body mass index, comorbidities and hospitalisations. Results Among 9589 individuals with RA (69% female, mean age of 58 years), 82 developed PE and 110 developed DVT (incidence rates, 1.5 and 2.1 per 1000 person-years). Compared with non-RA individuals (N=95 776), the age-, sex-and entry-time-matched RRs were 2.23 (95% CI 1.75 to 2.86) for PE and 2.20 (CI 1.78 to 2.71) for DVT. Adjusting for other covariates, the corresponding RRs were 2.16 (CI 1.68 to 2.79) and 2.16 (CI 1.74 to 2.69). The time-specific RRs for PE were 3.27, 1.88 and 2.35 for follow-up times of <1 year, 1-4.9 years, and >= 5 years, and corresponding RRs for DVT were 3.16, 1.82 and 2.32. Conclusions This population-based study indicates an increased risk of PE and DVT in RA, supporting increased monitoring of venous-thromboembolic complications and risk factors in RA, regardless of hospitalisation.