Background: Little information is available concerning risk factors for venous thromboembolism (VTE) in nonhospitalized patients.
Participants and methods: An epidemiologic case-control study of deep vein thrombosis (DVT) risk factors was conducted in 1272 outpatients by general practitioners. The case population (636 patients presenting with DVT) was paired with the control population (636 patients presenting with influenzal or rhinopharyngeal syndrome) according to sex and age. Deep vein thrombosis was to be documented by at least 1 objective test. Risk factors were classified into "intrinsic" ("permanent") and "triggering" ("transient") factors and were evidenced using univariate analysis.
Results: In the medical population, defined as patients who had not undergone surgery or application of a plaster cast to the lower extremities within the 3 weeks preceding inclusion (494 cases and 494 controls), intrinsic factors such as history of VTE, venous insufficiency, chronic heart failure, obesity, immobile standing position, history of more than 3 pregnancies, and triggering factors such as pregnancy, violent effort, or muscular trauma, deterioration of general condition, immobilization, long-distance travel, and infectious disease were significantly more frequent in the case patients than in the controls (odds ratio, >1; P<.05). In the overall population, additional risk factors were cancer, blood group A, plaster cast of the lower extremities, and surgery. In both populations, the number of risk factors per patient was greater in the case patients than in the controls.
Conclusion: Several risk factors for DVT were identified in medical outpatients presenting with DVT, and their comprehension may improve appropriateness and efficiency of the different methods available for thromboprophylaxis. Arch Intern Med. 2000;160:3415-3420.