Influence of Kidney Transplant Status on Warfarin Dose, Anticoagulation Control, and Risk of Hemorrhage

Study Design: To assess whether warfarin dose requirement, anticoagulation control, and risk of hemorrhage differ in kidney transplant recipients (KTRs) compared with patients without kidney transplants (non-KTRs). Design: Analysis of data from the Warfarin Pharmacogenetics Cohort, a prospective cohort of first-time warfarin users followed at two anticoagulation clinics. Setting: Two outpatient anticoagulation clinics at two large, academic, tertiary care hospitals. Patients: Adults aged 20 years or older starting warfarin for anticoagulation with a therapeutic international normalized ratio (INR) goal of 2–3 who were KTRs (n=65) or non-KTRs (n=1630). Measurements and Main Results: Warfarin dose requirement, anticoagulation control, and risk of hemorrhage were assessed in each group. KTRs required an approximately 20% lower warfarin dose (4.7 vs 5.6 mg/day, p=0.0005) compared with non-KTRs. Genetic variants had similar effects on dose in both groups. Mean percentage of time in therapeutic range (PTTR) was similar among KTRs and non-KTRs. Although the proportion of patients achieving good anticoagulation control (PTTR ≥ 60%) was low in both groups, it was similar among KTRs and non-KTRs. KTRs had a higher risk of major hemorrhage (hazard ratio 2.1, p=0.0081), but this difference was not statistically significant after controlling for kidney function, clinical, and genetic factors. Conclusion: KTRs initiating warfarin require lower doses and closer monitoring to optimize anticoagulation therapy. Additional studies are needed to confirm these findings.