Warfarin high-sensitivity — CYP2C9 + VKORC1
A CYP2C9 reduced-function allele combined with the VKORC1 high-sensitivity allele.
You have a slow version of one gene that clears the blood thinner warfarin, plus a version of another that makes warfarin extra-effective.
The two strongest pharmacogenetic predictors of warfarin dose are stacked here. If warfarin is ever prescribed, lower starting doses are essential to avoid over-anticoagulation. CPIC guidelines provide specific dose algorithms; please mention both findings to any prescribing clinician.
Together, these two DNA changes mean you would react strongly to even small doses of the blood thinner warfarin. If you're ever prescribed it, the starting dose needs to be lower than usual to avoid bleeding. Please mention both of these to any doctor planning to prescribe warfarin.
What this means
CYP2C9 metabolises warfarin; VKORC1 is its direct target. Reduced CYP2C9 activity means warfarin clears slowly; the high-sensitivity VKORC1 variant means a given drug level produces a larger anticoagulation effect. The combination is the textbook high-sensitivity warfarin phenotype. Many transplant centres and anticoagulation clinics now use genotype-guided dosing.
One of these genes (CYP2C9) clears warfarin out of your body; the other (VKORC1) is what warfarin acts on. Your CYP2C9 version clears the drug slowly, so it sticks around longer. Your VKORC1 version responds more strongly to whatever drug is there. The combination is the textbook example of being especially sensitive to warfarin, and many hospitals now adjust starting doses based on these two findings.
Caveats
- Most relevant only if warfarin or coumarin anticoagulants are prescribed.
- INR monitoring remains essential.
- DOAC anticoagulants (apixaban, rivaroxaban) are not affected by these variants.