2025 Southeastern Residency Conference

Title: Risk Factors related to Time in Therapeutic Range for Warfarin Patients in an Outpatient Cardiology Clinic


Authors: Anna Cooke, Ben Tabor, Marina Carter, Adam Pizzuti, Lauren Schultz


Objective: Determine which individual patient factors are associated with highter or lower time in therapeutic range related to warfarin therapy


Self-Assessment Question: Which individual patient factors correlate with a lower time in therapeutic range while on warfarin?


Background: Despite the emergence of new oral anticoagulants, warfarin remains a regularly utilized option for the prevention and treatment of venous thrombosis and thromboembolic events. While warfarin, a vitamin K antagonist, is an effective anticoagulant, it has several limitations due to its narrow therapeutic range, dose response variability, and numerous drug-drug and drug-food interactions. Therefore, to ensure optimal anticoagulation with warfarin, a patient’s international normalized ratio (INR) must be frequently monitored. Time in therapeutic range (TTR) is used to assess the percentage of time a patient on warfarin is within their target INR range, allowing clinicians to estimate a patient’s quality of anticoagulation. Certain patient characteristics exist that may lead to a higher or lower TTR while on warfarin for anticoagulation. The purpose of this study is to identify these individual risk factors in our patient population at Prisma Health to better warfarin management and help to identify those at greater risk for complications. 


Methods: This retrospective cohort study included patients aged 18 years and older on warfarin therapy for at least 30 days who were being managed by the Coumadin Clinic at Prisma Health Cardiology. To be included, patients had to have an INR goal range of 2.0-3.0 or 2.5-3.5 and have at least 3 INR values reported between November 1, 2023 and April 30, 2024 with INR values no greater than 60 days apart. The primary objective was to identify variables associated with lower or higher TTR related to warfarin therapy, such as race, warfarin indication, weight (kg), or history of thromboembolic events. The secondary objective was to determine the safety of warfarin therapy in patients with different TTR ranges. Statistical analysis will involve multivariate logistic regression and descriptive statistics.


Results: In progress


Conclusion: In progress