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Background: Percent time in therapeutic range (TTR) and international normalized ratio (INR) variability both measure warfarin control and are associated with outcomes independently. Here, we examine the advantages of a warfarin composite measure (WCM), which summarizes the 2 when measuring patient outcomes. We also examine how the measure chosen would affect anticoagulation clinic performance rankings., Methods and Results: We constructed WCM using an equally weighted method, adding standardized TTR to standardized log-transformed INR variability using 103 897 warfarin-experienced patients from 100 anticoagulation clinics. We examined the association of WCM with ischemic stroke, major bleeding, and fatal bleeding, using a subset of patients with atrial fibrillation (n=40 404). We divided patients into quintiles based on their level of control for TTR, log INR variability, and WCM. We calculated the hazard ratios for ischemic stroke, major bleeding, and fatal bleeding stratified by these quintiles. WCM hazard ratios for stroke and fatal bleeding showed the largest difference between excellent control and poorest control quintile compared with TTR and log INR variability, but not for major bleeding. In addition, we compared site rankings obtained using each of our 3 performance measures. Kappa scores for identifying outlier and nonoutlier clinics between WCM and its components were moderate (κ=0.56 for TTR and κ=0.62 for log INR variability) but was weak between TTR and log INR variability (κ=0.13)., Conclusions: WCM produces the largest range of risk for warfarin complications, widening the floor ceiling effects that limit the use of TTR and INR variability as separate measures. Anticoagulation clinics ranking changed considerably according to the anticoagulation measure that was selected.

Background: Among patients receiving warfarin, percent time in therapeutic range (TTR) and international normalized ratio (INR) variability predict adverse events individually. Here, we examined what is added to the prediction of adverse events by using both measures together., Methods and Results: We included 40 404 patients anticoagulated for atrial fibrillation, aged 65+, within the Veterans Health Administration. TTR and log-transformed INR variability were calculated for each patient. Our study outcomes were ischemic stroke and major bleeding, defined using International Classification of Diseases-9 codes. We estimated the hazard ratios (HRs) for the study outcomes using 3 nested Cox regression models, including (1) TTR or log INR variability separately; (2) TTR and log INR variability together; and (3) both predictors together plus an interaction term. We divided TTR into 3 categories (high, >70%; moderate, 50% to 70%; low, <50%) and log INR variability into 2 categories (stable and unstable). The reference groups high TTR and stable anticoagulation each denote good control. Higher log INR variability (ie, unstable control) predicted ischemic stroke (HR=1.45, P<0.001) and major bleeding (HR=1.57, P<0.001) independently, regardless of TTR levels. Our model with interaction terms showed that High log INR variability predicted a significantly higher risk for ischemic stroke and major bleeding compared with low log INR variability, at moderate TTR levels (HR= 1.27 and HR=1.29, respectively) and at high TTR levels (HR=1.55 and HR=1.56, respectively), but not at low TTR levels., Conclusions: Unstable anticoagulation predicts warfarin adverse effects independent of TTR. Moreover, knowledge about anticoagulation stability further stratifies the risk for adverse events at given levels of TTR., (© 2014 American Heart Association, Inc.)