Risk of Thromboembolism Varies, Depending on Category of Immobility in Outpatients

Study objective: Immobility predisposes to venous thromboembolism, but this risk may vary, depending on the underlying cause of immobility. Methods: This was a prospective, longitudinal outcome study of self-presenting emergency department (ED) patients who were from 12 hospitals and had suspected venous thromboembolism. Using explicit written criteria, clinicians recorded clinical features of each patient in the ED by using a Web-based data form. The form required one of 6 types of immobility: no immobility, general or whole-body immobility greater than 48 hours, limb (orthopedic) immobility, travel greater than 8 hours causing immobility within the previous 7 days, neurologic paralysis, or other immobility not listed above. Patients were followed for 45 days for outcome of venous thromboembolism, which required positive imaging results and clinical plan to treat. Odds ratios (ORs) were derived from logistic regression including 12 covariates. Results: From 7,940 patients enrolled, 545 of 7,940 (6.9%) were diagnosed with venous thromboembolism (354 pulmonary embolism, 72 deep venous thrombosis, 119 pulmonary embolism and deep venous thrombosis). Risk of venous thromboembolism varied, depending on immobility type: limb (OR=2.24; 95% confidence interval [CI] 1.40 to 3.60), general (OR=1.76; 95% CI 1.26 to 2.44), other (OR=1.97; 95% CI 1.25 to 3.09), neurologic (OR=2.23; 95% CI 1.01 to 4.92), and travel (OR=1.19; 95% CI 0.85 to 1.67). Other significant risk factors from multivariate analysis included age greater than 50 years (OR =1.5; 95% CI 1.25 to 1.82), unilateral leg swelling (OR=2.68; 95% CI 2.13 to 3.37), previous venous thromboembolism (OR=2.99; 95% CI 2.41 to 3.71), active malignancy (OR=2.23; 95% CI 1.69 to 2.95), and recent surgery (OR=2.12; 95% CI 1.61 to 2.81). Conclusion: In a large cohort of symptomatic ED patients, risk of venous thromboembolism was substantially increased by presence of limb, whole-body, or neurologic immobility but not by travel greater than 8 hours. These data show the importance of clarifying the cause of immobility in risk assessment of venous thromboembolism. [Ann Emerg Med. 2009;54:147-152.]