Outcomes and predictors of very stable INR control during chronic anticoagulation therapy
Daniel M. Witt13, Thomas Delate2,3, Nathan P. Clark1,2, Chad Martell2, Thu Tran2, Mark A. Crowther4, David A. Garcia5, Walter Ageno6, Elaine M. Hylek7, on behalf of the Warfarin Associated Research Projects and other EnDeavors (WARPED) Consortium
1 Kaiser Permanente Colorado Clinical Pharmacy Anticoagulation Service, Lafayette; 2 University of Colorado School of Pharmacy, Denver; 3 Kaiser Permanente Colorado Clinical Pharmacy Research Team, Aurora; 4 McMaster University, Hamilton, ON; 5 University of New Mexico School of Medicine, Albuquerque; 6 University of Insubria, Varese, Italy; and 7 Boston University School of Medicine, MA
For patients on warfarin therapy, an international normalized ratio (INR) recall interval not exceeding 4 weeks has traditionally been recommended. Less frequent INR monitoring may be feasible in stable patients. We sought to identify patients with stable INRs (defined as having INR values exclusively within the INR range) and comparator patients (defined as at least one INR outside the INR range) in a retrospective, longitudinal cohort study. Occurrences of thromboembolism, bleeding, and death were compared between groups. Multivariate logistic regression models were used to identify independent predictors of stable INR control. There were 2504 stable and 3569 comparator patients. The combined rates of bleeding and thromboembolism were significantly lower in stable patients. Independent predictors of stable INR control were age older than 70 years and the absence of comorbid heart failure and diabetes. Stable patients were significantly less likely to have target INR of 3.0 or higher or chronic diseases. We hypothesize that many patients demonstrating stable INR control could be safely treated with INR recall intervals greater than the traditional 4 weeks.