Hematology consult: high-sensitivity warfarin genotype

Warfarin sensitivity genotyping should be considered in patients who require multiple dosing adjustments to maintain a therapeutic international normalized ratio (INR)--patients with a history of bleeding/thrombosis when taking warfarin or patients who are being started on warfarin therapy for the first time. Studies showed that individuals with genetic variants require a longer time to achieve stable dosing, have more INR measurements that are above therapeutic range, and experience more frequent bleeding events than individuals with normal genotypes. This information prompted development of dosing algorithms based on genotypes in an attempt to more accurately predict warfarin dose and avoid such complications. We report herein a patient with an exaggerated response to warfarin, who was subsequently diagnosed with a high-sensitivitywarfarin genotype. Genetic testing for warfarin sensitivity polymorphisms is currently available, and may decrease event rates for bleeding and/orthromboembolismwhen used to guide dosing. Notwithstanding, randomized controlled trials are awaited to determine the true impact of this testing on clinical outcomes and its cost-effectiveness.