Background: Time in therapeutic range (TTR) measures the quality of vitamin K antagonist (VKA) anticoagulation. The dichotomized SAMe-TT2-R2 score can predict, among patients with atrial fibrillation, if adequate TTR is likely to be achieved.
Methods: We validated the score in patients with acute venous thromboembolism (VTE) randomized to the warfarin arm of the Hokusai-VTE trial: a total of 3,874 patients were included in the analysis. The primary efficacy and safety outcomes were symptomatic recurrent VTE and the composite of major or clinically-relevant-non-major bleeding, respectively.
Results: The rates of recurrent VTE and bleeding events were higher in patients with a TTR below the median (TTR< 66% versus ≥66%) resulting in an absolute risk difference [ARD] of +0.5% (95%CI 0%; +1.1%) and +2.2% (0.9%; +3.5%), respectively. Patients with a high SAMe-TT2-R2 score (76% of total) had lower median TTR than patients with a low SAMe-TT2-R2 score (64.7% versus 70.7%, respectively). The SAMe-TT2-R2 score had poor negative (0.59) and positive (0.52) predictive values (TTR cut-off 66%), and exhibited poor discrimination (c-statistic 0.58). Patients with a high (versus low) SAMe-TT2-R2 score had similar rates of recurrent VTE (ARD 0% [-0.6%; +0.7%]) and bleeding (ARD +1.3% [-0.1%; +2.7%]).
Conclusions: In the setting of acute VTE, the SAMe-TT2-R2 score showed unsatisfactory discrimination and predictive value for individual TTR: therefore, the choice of starting a patient on VKA cannot be based on this parameter. Since the SAMe-TT2-R2 score did not correlate well with clinical outcomes, its routine use in acute VTE may not translate into clinical usefulness.
