See the section on self-monitoring and self-management of vitamin K antagonists. [2021]. 1.6.6 For adults with atrial fibrillation who are already taking a vitamin K antagonist and are stable, continue with their current medication and discuss the option of switching treatment at their next routine appointment, taking into account the person's time in therapeutic range. 1.6.7 Do not offer stroke prevention therapy with anticoagulation to people aged under 65 years with atrial fibrillation and no risk factors other than their sex (that is, very low risk of stroke equating to a CHA2DS2-VASc score of 0 for men or 1 for women). [2021] 1.6.8 Do not withhold anticoagulation solely because of a person's age or their risk of falls. [2021] For a short explanation of why the committee made these recommendations and how they might affect practice, see the rationale and impact section on stroke prevention. Full details of the evidence and the committee's discussion are in evidence review G1: anticoagulant therapy for stroke prevention in people with atrial fibrillation and evidence review G2: anticoagulant therapy health economics analysis. Assessing anticoagulation control with vitamin K antagonists 1.6.9 Calculate the person's time in therapeutic range (TTR) at each visit. When calculating TTR: use a validated method of measurement such as the Rosendaal method for computer-assisted dosing or proportion of tests in range for manual dosing exclude measurements taken during the first 6 weeks of treatment calculate TTR over a maintenance period of at least 6 months. [2014] 1.6.10 Reassess anticoagulation for a person whose anticoagulation is poorly controlled shown by any of the following: 2 INR values higher than 5 or 1 INR value higher than 8 within the past 2 INR values less than 1.5 within the past 6 months TTR less than 65%. 