Incidence and risk factors of thromboembolism in systemic lupus erythematosus: A comparison of three ethnic groups

Objective. To compare the incidence and risk factors for thromboembolic events in systemic lupus erythematosus (SLE) patients of different ethnic backgrounds. Methods. SLE patients who were newly diagnosed or were referred within 6 months of diagnosis between 1996 and 2002 were prospectively followed up for the occurrence of thromboembolic events. Cumulative hazard and risk factors for thromboembolism were evaluated and compared among patients of different ethnic origins. Results. We studied 625 patients who fulfilled the American College of Rheumatology criteria for SLE (89% women): 258 Chinese, 140 African Americans, and 227 Caucasians. The mean ± SD age at SLE diagnosis was 35.7 ± 14 years. After a followup of 3,094 patient-years, 48 arterial events and 40 venous events occurred in 83 patients. The overall incidence of arterial and venous thromboembolism was 16/1,000 patient-years and 13/1,000 patient-years, respectively. The cumulative hazard of arterial events at 60 months after the diagnosis of SLE was 8.5%, 8.1%, and 5.1% for the Chinese, African Americans, and Caucasians, respectively. The corresponding cumulative risk of venous events was 3.7%, 6.6%, and 10.3%, respectively (P = 0.008 for Chinese versus Caucasians, by log rank test). Smoking, obesity, antiphospholipid antibodies, and use of antimalarial agents and exogenous estrogens were less frequent in the Chinese patients. In Cox regression models, low levels of high-density lipoprotein (HDL) cholesterol, Chinese ethnicity, oral ulcers, and serositis predicted arterial events, whereas male sex, low levels of HDL cholesterol, antiphospholipid antibodies, non-Chinese ethnicity, obesity, renal disease, and hemolytic anemia predicted venous events. Conclusion. There are ethnic differences in the incidence of arterial and venous thromboembolism in patients with SLE that cannot be fully explained by the clinical factors studied. Further evaluation of other genetic and immunologic factors is warranted.