PURPOSE: To evaluate real-world clinical practice INR patterns and outcomes associated with warfarin use in patients managed in a university-based antithrombosis clinic (ATC).
METHODS: We analyzed a retrospective observational cohort of patients undergoing total knee or hip replacement (TKR or THR), receiving warfarin prophylaxis within 24 hours of surgery, who were referred to the ATC for anticoagulation management (January 1998-January 2009; follow-up: 3 months post-surgery).
RESULTS: 400 patients (male: 68%) were evaluated (TKR: 55%; THR: 45%). Mean age (±SD) was 58.4±12.5 years. Mean length of hospital stay was 5.0±1.9 days, and mean length of warfarin therapy was 50±21 days (including outliers). Mean time required to reach therapeutic INR range of 2-3 was 10.0±9.1 days, with similar results obtained for THR and TKR. The within-patient proportion of INR levels spent in therapeutic range was 28±18%, while the proportion in extended therapeutic range (INR 1.8-3.2) was 39.2±20.5%. The within-patient proportion of INR levels spent below therapeutic range was 65±22.6% for INR < 2 and 37.7±21.6% for INR < 1.5. Major bleeding occurred in 2 (0.45%) patients. Objectively confirmed, symptomatic venous thromboembolism (VTE) occurred in 16 (4%) patients (8 inpatients, 8 outpatients), with a total of 14 (87.5%) events occurring at INR < 2, versus 2 (12.5%) at INR >2 (p< 0.05).
CONCLUSION: Despite close monitoring, warfarin use was associated with significant time spent below recommended anticoagulant levels, which in turn was associated with higher rates of symptomatic VTE. That the majority of events occurred at INR levels < 2 may indicate the need for more aggressive anticoagulation in the acute post-operative phase.
CLINICAL IMPLICATIONS: Our results highlight the challenges of warfarin management in real life clinical practice after TKR and THR, despite close monitoring via a centralized management model. In addition, our data stress the importance of attaining and maintaining the American College of Chest Physicians recommended INR range of 2-3 after TKR and THR.
DISCLOSURE: Edith Nutescu, Grant monies (from sources other than industry) Dr. Nutescu is supported by the University of Illinois at Chicago (UIC) Center for Clinical and Translational Science (CCTS), Award Number KL2RR029878 from the National Center For Research Resources. Dr.’s Galanter and Lambert were supported by grant U18HS016973 from the Agency for Healthcare Research and Quality The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center For Research Resources, the National Institutes of Health or the Agency for Healthcare Research and Quality.; Grant monies (from industry related sources) Funding for this research was provided by Johnson and Johnson Health Economics and Outcomes Research.; Employee Brahim Bookhart and Samir Moody are employees of Johnson and Johnson Health Economics and Outcomes Research.; No Product/Research Disclosure Information