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Background:The association between peripheral leukocyte count and bleeding events in nonvalvular atrial fibrillation (NVAF) patients treated with dabigatran remains unclear.This study aimed to explore the association between leukocyte count and bleeding events after excluding other confounders in NVAF patients taking dabigatran.Methods:A total of 851 NVAF patients treated with dabigatran (110 mg bid) were recruited from 12 centers in China from February 2015 to December 2017.Follow-up was completed by May 2018.The exposure and outcome variables were leukocyte count measured at baseline and the number of bleeding events within the subsequent 6 months.Multivariate Cox proportional hazards models were constructed to analyze independent associations,and a Cox proportional hazards regression with cubic spline functions and smooth curve fitting (penalized spline method) was used to address nonlinearity between leukocyte count and bleeding.The inflection point was calculated using a recursive algorithm,and then a two-piecewise Cox proportional hazards model for both sides of the inflection point was constructed.Results:During 6-month follow-up,87 participants occurred bleeding events.For every 1 x 109/L increase in leukocyte count,the risk of bleeding increased by 11％ (hazard ratio [HR]:1.11,95％ confidence interval [CI]:0.99-1.25).The smooth curve showed nonlinear relationship between leukocyte count and bleeding events.The inflection point of the leukocyte count was 6.75 × 109/L.For leukocyte counts ＜ 6.75 x 109/L,the HR (95 ％ CI) was 0.88 (0.69-1.13),and for leukocyte counts ≥ 6.75 × 109/L,the HR (95％ CI) was 1.28 (1.09-1.51).Conclusion:This study found a J-shaped association between baseline leukocyte count and risk of bleeding in NVAF patients treated with dabigatran.