BACKGROUND:

There has been great interest in optimizing prophylaxis against venous thromboembolism (VTE) in the hospital setting. However, data from earlier studies suggest that most VTEs occur in the outpatient setting. The purposes of this observational study were to describe the frequency of VTEs occurring in the outpatient setting, characterize the prevalence of previously identified risk factors for VTE, and identify previous use of VTE prophylaxis.

METHODS:

The medical records of residents from the Worcester metropolitan area diagnosed as having International Classification of Diseases, Ninth Revision codes consistent with possible VTE during 1999, 2001, and 2003 were independently validated and reviewed by trained abstractors.

RESULTS:

A total of 1897 subjects had a confirmed episode of VTE. In all, 73.7% of patients developed VTE in the outpatient setting; a substantial proportion of these patients had undergone surgery (23.1%) or hospitalization (36.8%) in the preceding 3 months. Among these patients, 67.0% experienced VTE within 1 month of the preceding hospital encounter. Other major risk factors for VTE in the outpatient setting included active malignant neoplasm (29.0%) or previous VTE (19.9%). Among 516 patients with a recent hospitalization who subsequently developed VTE, less than half (42.8%) had received anticoagulant prophylaxis for VTE during that visit.

CONCLUSIONS:

More VTEs were diagnosed in the 3 months following hospitalization than during hospitalization. Efforts to improve in-hospital use of VTE prophylaxis may help decrease the incidence of outpatient VTE. However, given the shortening of hospital stays, studies of extended VTE prophylaxis following hospital discharge are warranted.