Warfarin dose sensitivity

Warfarin dosing is genetic by nature: VKORC1 (the drug's target), CYP2C9 (which clears it), and CYP4F2 together set how much a person needs. Clinical dosing reads all of them at once, so they belong in one panel rather than apart.

Possible results

Needs a markedly lower warfarin dose. You carry a strong combination of warfarin-sensitivity variants (two low-dose copies of VKORC1, a strong reduced-function version of CYP2C9, or both genes together), so your body needs noticeably less warfarin to reach a safe blood-thinning level. People with this pattern over-thin and bleed more easily on a standard starting dose, which is exactly why doctors use genotype-guided dosing. This is informational only, never a reason to change a prescription yourself.

Needs a somewhat lower warfarin dose. You carry one warfarin-sensitivity variant (a single low-dose copy of VKORC1 or one reduced-function version of CYP2C9), so you likely need a modestly lower warfarin dose than average. It's a nudge toward careful dosing and closer monitoring early on, not a dramatic change, and only matters if warfarin is ever prescribed.

Typical warfarin dose expected. You don't carry the common variants that make people unusually sensitive or resistant to warfarin, so from what these genes show a standard starting dose is a reasonable expectation. Age, weight, diet and other drugs still shape the right dose, so monitoring always guides treatment.

Needs a slightly higher warfarin dose. You don't carry the sensitivity variants, and you do carry the CYP4F2 variant that slightly raises how much warfarin people tend to need. The effect is small, on the order of an extra milligram a day, and is the opposite direction from the VKORC1 and CYP2C9 genes.

Evidence & sources

This panel reads VKORC1 -1639, CYP2C9*2, CYP2C9*3, CYP2C9*5, CYP2C9*8, CYP2C9*11, CYP4F2*3.

Reads VKORC1, the common reduced-function versions of CYP2C9, and CYP4F2. Some rarer versions of CYP2C9 are not tested, so a typical result does not rule them out.

CPIC provides dosing guidance for warfarin based on this gene.

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