 Cytochrome P450 2C9 genotyping can identify mutations associated with impaired warfarin metabolism. The CYP2C9 genotype accounts for about 10 of warfarin dose variance. Vitamin K receptor polymorphism testing can identify whether patients require low, intermediate, or high doses of warfarin. Five common vitamin K receptor gene haplotypes account for about an additional 25 of warfarin dose variance. 