The stability of anticoagulation is a key indicator for assessing the efficacy of warfarin in atrial fibrillation, which is an important anticoagulation therapy for the disease. Existing studies show that the eligible rate of stability of warfarin anticoagulation is rather unsatisfactory, and there are few studies on how to effectively calculate the stability of the treatment. Moreover, methods recommended in guidelines for estimating the stability of warfarin anticoagulation have limitations, with no effective suggestions for calculating stability of warfarin anticoagulation in the early stage of treatment.

To assess the practical efficacy of "double six definitions" in guideline-recommended method for estimating the stability of warfarin anticoagulation〔using INR data monitored for at least six months but excluding the data within the first six weeks〕, providing a reference for improving the method for calculating the stability of warfarin anticoagulation.

Participants with persistent non-valvular atrial fibrillation (n=126) were recruited from Jiujiang No.1 People's Hospital from January 2019 to December 2020. All of them received warfarin anticoagulant therapy and outpatient or inpatient follow-ups for understanding the coagulation status. The stability of warfarin anticoagulation was described using time in therapeutic range (TTR) calculated by different methods, namely using INR data in a 7-12-month follow-up period with or without removal of INR data in the first 6 weeks, and INR data in 12 consecutive months of follow-up with or without removal of INR data in the first 6 weeks, and the results were compared with the TTR calculated by "double six definitions".

Calculating the TTR using INR data of 7-12 months: there were no significant differences between the TTR calculated using INR data of 7, 8, 9, 10, 11 or 12 months with and without the first 6-week INR data (P>0.05) . Calculating the TTR using INR data of 12 consecutive months: when INR data in the first 6 weeks of follow-up were removed, the TTR at the first and second months of follow-up could not be calculated using the set formula, and it was deemed to be 0. There was significant difference between TTR calculated with and without INR data in the first 6 weeks at 1- or 2-month follow-up (P<0.001) . There was no significant difference between TTR calculated with and without INR data in the first 6 weeks at 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 11- or 12-month follow-up (P > 0.05) . The TTR calculated using INR data of 7 to 12 months of follow-up was similar to that calculated using INR data at one time point of the second half period (7 to 12 months) within the 12-month follow-up under the condition of removing the INR data of the first 6 weeks (P>0.05) , and the same thing was found when the INR data of the first 6 weeks were not removed (P>0.05) . Furthermore, there were no significant differences in TTR calculated using INR data of 7 to 12 months of follow-up and using INR data of 12 consecutive months of follow-up regardless of whether the INR data of the first 6 weeks were removed or not (P>0.05) .

In the calculation of the stability of warfarin anticoagulation in atrial fibrillation, the INR data in the first 6 weeks might be included, and the baseline follow-up time for monitoring INR might not necessarily be greater than 6 months.