Correlation between warfarin dose (μg/kg per day), INR, and genotypes at codon 181 of exon 4.

The warfarin dose requirement (left axis) was significantly higher in patients carrying the heterozygous ATT/CTT alleles (lane 2) than in those carrying the homozygous ATT/ATT alleles (lane 1) (P < .001, Mann-Whitney U test). There was, however, no difference in INR between these 2 groups of patients (right axis).