Effect of age on international normalized ratio at the time of major bleeding in patients treated with warfarin

STUDY OBJECTIVES: Because the risk of major bleeding associated with warfarin increases with increasing international normalized ratio (INR) as well as with advanced age, we evaluated the association between age and INR in patients with major bleeding events related to anticoagulation with warfarin. DESIGN: Retrospective record review. SETTING: Two university-affiliated anticoagulation clinics. PATIENTS: Sixty-six patients (mean age 61.2 yrs, range 21-90 yrs) receiving warfarin therapy who experienced major bleeding, defined as bleeding requiring hospitalization, during a 20-month index period. MEASUREMENTS AND MAIN RESULTS: In patients aged 65 years or older, the mean INR at the time of a major bleeding event was significantly lower than that in patients younger than 65 years (INR 3.1 vs 4.2, respectively; p=0.01). For every 1-year increase in age, mean INR at the time of a major bleeding event decreased by 0.03 (p=0.02). CONCLUSION: Patients aged 65 years or older experience warfarin-related major bleeding events at a mean INR 1.1 units lower (95% confidence interval -1.9 to -0.27) than patients younger than 65 years. Older patients may require more aggressive management of overanticoagulation to minimize the risk of major bleeding.