Novel Warfarin Composite Quality Measure
How well does a novel warfarin composite measure (WCM) incorporating the percentage of time in the therapeutic range (TTR) and international normalized ratio (INR) variability predict patient outcomes and affect anticoagulation clinic performance rankings?
The WCW, as calculated using an equally weighted and standardized TTR to a log-transformed and standardized INR variability measure, was derived among 103,897 warfarin-experienced patients in 100 Veterans Affairs anticoagulation clinics. WCM association with ischemic stroke, major bleeding, and fatal bleeding was explored in a subcohort of patients with atrial fibrillation (n = 40,404). Hazard ratios for ischemic stroke, major bleeding, and fatal bleeding were compared across quintiles of patients for each of the warfarin quality measures (TTR, log-transformed INR variability, and WCW).
In the atrial fibrillation subcohort, 3.1% of patients experienced an ischemic stroke, 6.4% experienced major bleeding, and 0.9% experienced fatal bleeding (a subset of major bleeding). Mean TTR was 63.6% (standard deviation, 21.2%) and ranged from 37.6% to 87.2% in the worst and best quintiles. Hazard ratios (HR) for stroke and fatal bleeding had the largest difference between the best and worst quintiles of warfarin control when using WCM (HR, 2.41; 95% confidence interval [CI], 2.01-2.92) as compared to TTR (HR, 2.10; 95% CI, 1.76-2.51) or INR variability (HR, 1.74; 95% CI, 1.46-2.08). There was no meaningful difference in HR difference between the WCM (HR, 1.95; 95% CI, 1.72-2.21) and TTR (HR, 1.99; 95% CI, 1.79-2.25).
The authors concluded that WCM produces the largest range of risk for warfarin complications, broadening existing ranges from TTR and INR variability.
While TTR is universally used to describe the quality of warfarin therapy in anticoagulated patients, it has some limited ability to predict individual risk of bleeding or ischemic stroke. The authors demonstrate that incorporating both the TTR and an INR variability measure into a single WCM score has broader risk stratification for ischemic stroke and fatal bleeding outcomes than TTR alone. However, limited access to real-time TTR, INR variability, or the new WCM measure will limit clinical application. However, anticoagulation providers may consider calculating WCM to identify their most ‘at risk’ patient who may benefit from closer monitoring and/or further support to avoid unwanted bleeding or thromboembolic events.
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