Evaluation of SAMe-TT2R2 Score on Predicting Success With Extended-Interval Warfarin Monitoring

Background: In patients with stable international normalized ratios, 12-week extended-interval warfarin monitoring can be considered; however, predictors of success with this strategy are unknown. The previously validated SAMe-TT2R2 score (considering sex, age, medical history, treatment, tobacco, and race) predicts anticoagulation control during standard follow-up (every 4 weeks), with lower scores associated with greater time in therapeutic range. Objective: To evaluate the ability of the SAMe-TT2R2 score in predicting success with extended-interval warfarin follow-up in patients with previously stable warfarin doses. Methods: In this post hoc analysis of a single-arm feasibility study, baseline SAMe-TT2R2 scores were calculated for patients with 1 extended-interval follow-up visit. The primary analysis assessed achieved weeks of extended-interval follow-up according to baseline SAMe-TT2R2 scores. Results: A total of 47 patients receiving chronic anticoagulation completed a median of 36 weeks of extended-interval follow-up. The median baseline SAMe-TT2R2 score was 1 (range 0-5). Lower SAMe-TT2R2 scores appeared to be associated with greater duration of extended-interval follow-up achieved, though the differences between scores were not statistically significant. No individual variable of the SAMe-TT2R2 score was associated with achieved weeks of extended-interval follow-up. Analysis of additional patient factors found that longer duration (24 weeks) of prior stable treatment was significantly associated with greater weeks of extended-interval follow-up completed (P = 0.04). Conclusion and Relevance: This pilot study provides limited evidence that the SAMe-TT2R2 score predicts success with extended-interval warfarin follow-up but requires confirmation in a larger study. Further research is also necessary to establish additional predictors of successful extended-interval warfarin follow-up.