Complications of warfarin therapy: causes, costs, and the role of the anticoagulation clinic.

CONTEXT Anticoagulation with warfarin requires careful management to avoid hemorrhage or thrombosis. The anticoagulation clinic has been suggested as a mechanism to reduce complications related to anticoagulation. OBJECTIVE To report our experience with anticoagulation complications, the cost of subsequent care, and the role of the anticoagulation clinic. DESIGN Sequential patients who were receiving warfarin within a period of 4 months were followed to identify warfarin-related adverse events. An independent examiner reviewed medical records to determine whether events were preventable and to identify possible causes. Hospital-based accounting data were used to determine attributable costs. PATIENTS 306 patients who received warfarin prescriptions at a rural Vermont university-affiliated VA hospital with an established anticoagulation clinic. RESULTS 91% (278) of patients received follow-up at the anticoagulation clinic, and the remaining 9% (28) were followed by VA physicians without involving the anticoagulation clinic. A total of 12 patients had adverse events associated with either sub- or supratherapeutic international normalized ratios, with an attributable cost of approximately $90,000; 8 of these patients were not enrolled in the anticoagulation clinic. Thus, the estimated relative risk for adverse events for patients not at the clinic, compared with those who were, was almost 20 (95% CI, 6.4 to 61.8). Review of the remaining 4 patients revealed that their problems were attributable either to missed appointments or lack of coordination between other providers and the anticoagulation clinic. CONCLUSIONS Establishing an anticoagulation clinic is only the first step toward reducing complications related to anticoagulation. The larger challenge is ensuring that patients use the anticoagulation clinic and that providers communicate with it. Our results suggest that our institution could invest considerable resources to meet this challenge and still save money.