Intensity of Anticoagulation with Warfarin and Risk of Adverse Events in Patients Presenting to the Emergency Department

BACKGROUND: The ability of patients receiving warfarin to maintain an international normalized ratio (INR) within the desired therapeutic range is important for both efficacy and risk of adverse events. It is unclear whether the desired INR is maintained in patients receiving warfarin who present to the emergency department (ED) and whether they have a higher rate of adverse events. OBJECTIVE: To evaluate the intensity of anticoagulation with warfarin and the risk of bleeding and thromboembolic complications in patients in the ED. METHODS: A prospective observational study was performed using a convenience sample of patients receiving warfarin and presenting to the ED over an 18-week period. Data were collected using a standardized form that included chief complaint, history of present illness, past medical history, medication history, and allergy status. Information from the physical examination, laboratory results, and other diagnostic tests obtained as part of routine assessment in the ED, was used as necessary. The primary outcome was the proportion of patients whose INR was within, above, or below the desired therapeutic range. Bleeding complications and thromboembolic events were recorded in an attempt to determine the relationship between the intensity of anticoagulation and adverse outcomes. RESULTS: Two hundred one patients were included, with a mean (SD) age of 74.0 (13.2) years; 53.7% were female. Primary indications for warfarin were atrial fibrillation (75.6%) and venous thromboembolic disease (14.9%). A therapeutic INR was observed in 88 patients (43.8%; 95% CI 37.1 to 50.7), while 45 patients (22.4%; 95% CI 17.2 to 28.7) and 68 patients (33.8%; 95% CI 27.6 to 40.6) had subtherapeutic and supratherapeutic INRs, respectively. Overall, there were 28 (18 major and 10 minor) bleeding complications (13.9%; 95% CI 9.8 to 19.4) and 4 thromboembolic events (2.0%; 95% CI 0.6 to 5.2). Among patients with a bleeding complication, 14 (50.0%) had a supratherapeutic INR, while 2 patients who experienced a thromboembolic event (50.0%) had a subtherapeutic INR. CONCLUSIONS: The majority of patients receiving warfarin on presentation to the ED had INRs outside the desired therapeutic range. By establishing the impact of warfarin-related adverse events in this population, focused interventions can be established in this setting to address factors that can be targeted to reduce these events.