An easy-to-use tool to flag patients at risk of poor INR control:A streak of subtherapeutic INRs

Introduction: Vitamin K antagonist therapy is safest and most effective with a high time within the therapeutic range (TTR). The TTR is difficult to calculate in the consultation room, therefore physicians need an easier-to-use tool to predict poor VKA control. We explored the prognostic value of subtherapeutic INRs on future TTR in two settings: (1) Clinical review setting, where a physician (bi) annually reviews a patient and uses the INRs since the last visit to predict the TTR up to the next visit; (2) Day-to-day INR management setting, where every new INR measurement prompts a new prediction over the next 90 days. Materials and methods: Retrospective cohort of 17,711 patients from a dedicated thrombosis service, using acenocoumarol (target range 2.0-3.0), with a "streak" defined as four consecutive INRs (1) Odds ratios of any streak in the last 180 days or 1 year on a TTR <45% over the same period in the future; (2) Odds ratio of a current streak on a TTR <45% over the next 90 days. Results and conclusions: Clinical review setting: The occurrence of any streak in the last 180 days or 1 year increased the odds of a TTR <45%: ORs 2.84 (95% CI 2.41-3.34) and 3.25 (95% CI 2.72-3.87), respectively. Day-to-day INR management setting: A current streak increases the odds of poor TTR over the next 90 days 3.58 (95% CI 2.64-4.87) fold. We conclude that a streak of four consecutive subtherapeutic INRs can aid physicians in flagging at-risk patients