Patient Outcomes with Warfarin Therapy after Hip and Knee Replacement: Comparison of Two Models of Care

The first objective of the study was to examine the association between race of the patients and their referral to anticoagulation clinic compared to orthopedic clinic for venous thromboembolism prophylaxis (VTE) post-surgery. The second objective was to compare time in therapeutic range (TTR) in patients receiving warfarin therapy between anticoagulation clinic and orthopedic clinic. We conducted a retrospective, observational study of patients who underwent hip or knee replacement surgery at University of Illinois Hospital and Health Sciences System (UIHHSS) between the years 2000 and 2009 and were referred to either anticoagulation clinic or orthopedic clinic at UIHHSS for post-surgical prophylaxis. There were 294 patients referred to anticoagulation clinic and 573 to orthopedic clinic. The majority of the study cohort patients were female (68.3%) and average age of the cohort was 59 years. Compared to Caucasians, African Americans (ORadj=1.543, 95% CI =0.929-2.563) and Hispanics (ORadj=4.244, 95% CI =2.378-7.574) were more likely to be referred to anticoagulation clinic whereas others (ORadj=0.164, 95% CI =0.050-0.545) were less likely to be referred to anticoagulation clinic adjusting for the covariates. The adjusted mean TTR was 8.96% higher after matching on propensity scores, 8.79% higher after matching covariates, 9.02% higher after applying inverse probability weighting and 9.08% higher after applying inverse probability weighting combined with regression adjustment for patients receiving warfarin prophylaxis at anticoagulation clinic. For the overall group, the adjusted mean TTR was 6.60% higher after applying inverse probability weighting and 7.1% higher after applying inverse probability weighting combined with regression adjustment for those referred to anticoagulation clinic compared to those referred to orthopedic clinic. Our study adds to the existing body of literature on anticoagulation models of care for patients receiving warfarin therapy. We found that race adjusting for covariates influenced the patient referral pattern to outpatient clinics for receiving post surgery prophylaxis. In addition, we found that patients in anticoagulation clinic have a higher TTR for receiving a short term VTE prophylaxis compared to routine model of care. Future research is needed to understand the impact of anticoagulation care in a larger diverse sample of patients receiving warfarin therapy.