Self-testing and clinical outcomes in Black and White patients on warfarin for atrial fibrillation or venous thromboembolism.

Background: Warfarin management requires frequent international normalized ratio (INR) testing. Self-testing may reduce this burden and improve INR control and outcomes. However, concerns exist about variability in utilization and the effectiveness of self-testing across different patient groups. Objectives: This study aimed to evaluate INR self-testing utilization and clinical outcomes in Black and White warfarin-treated patients. Methods: In this retrospective, observational study, Black and White patients who were using warfarin for atrial fibrillation or venous thromboembolism (April 2012 to July 2024) were identified from the Michigan Anticoagulation Quality Improvement Initiative registry. INR control and outcomes were compared between self-testers and non-self-testers. Rates were adjusted by inverse probability weighting; comparisons between racial groups used the negative binomial model. Major and nonmajor bleeding events were defined based on the International Society on Thrombosis and Haemostasis criteria. Moderation analysis examined whether race influences self-testing's safety and effectiveness. Results: Among 5903 warfarin-treated patients (20.5% Black, 79.5% White), self-testing was used by fewer than 1 in 7 patients (15.3% White, 10.1% Black). Self-testers had higher adjusted time in therapeutic range (TTR; 65.3% vs 59.8%; Conclusion: Self-testing was utilized infrequently, especially among Black patients, but was associated with better INR control and less bleeding than traditional INR testing. Increased utilization and support of self-testing may improve patient outcomes.