Racial differences in anticoagulation control and risk of hemorrhage among warfarin users

Purpose: Factors such as comorbidities, age, genetics, and concurrent medications have been shown to alter warfarin’s dose, anticoagulant effect and associated hemorrhage risk.  However, the influence of race on INR control and hemorrhagic risk in warfarin users is not well documented.  Herein we assess whether there are differences in percent time spent in therapeutic INR range (2-3) and the risk of hemorrhagic complications in Blacks vs. Whites.

Methods: Patients on chronic warfarin therapy (n=1260) were prospectively followed from initiation of therapy. Detailed medical history was documented at baseline and monthly updates documented dose changes, INR control and occurrence of hemorrhagic complications. Racial differences in percent time in target range was assessed using Proc Mixed and risk of hemorrhage was assessed using Cox proportional hazards regression analysis in SAS version 9.2.

Results: In comparison to Whites, Blacks spent less days within therapeutic INR range (51.85% vs. 58.65%; p <0.0001) and more days below (49.96% vs. 36.64%; p = 0.0002) and above (18.92% vs. 16.12%; p = 0.0449) therapeutic INR range.  In comparison to Whites, Blacks had a lower risk of a minor hemorrhage (HR 0.76; CI 0.64, 0.90; p = 0.0017).  For major hemorrhage, Blacks had a higher risk (HR 1.67; CI 1.13, 2.48; p = 0.0104).

Conclusion: Blacks spent more time above recommended INR therapeutic range and had a higher risk of major hemorrhage.  Factors explaining these differences could include clinical and genetic factors or differences in lifestyle, diet, medication adherence and access to care.