Warfarin Sensitivity Genotyping

Test Overview 
Warfarin (Coumadin) is an anticoagulant used to prevent or treat clotting disorders associated with venous thrombosis, pulmonary embolism, atrial fibrillation, cardiac valve replacement, stroke and acute myocardial infarction. It is a vitamin K antagonist composed of S- and R- isomers.

The more potent S-warfarin is metabolized by Cytochrome 450 isoenzyme, encoded by CYP2C9 gene. Warfarin exerts its anticoagulant effect by inhibiting its target enzyme Vitamin K epoxide reductase (VKOR), encoded by Vitamin K epoxide reductase subunit 1 (VKOR1) gene. Genetic variations in the CYP2C9 and VKOR1 genes can affect warfarin’s efficacy and dose required to achieve stable International Normalized Ratio (INR). Specifically, two variants in the CYP2C9 gene (CYP2C9*2 and CYP2C9*3) result in an enzyme with reduced activity, leading to increased active warfarin levels. A variant in the VKORC1 gene (VKORC1- 1639 G>A) can lead to reduced gene expression resulting in decreased level of VKOR. Together, these three variants can account for 40 to 70% of the variability in warfarin dose.

Reason for referral 
Optimization of warfarin dose based on different genotypes of VKORC1 and CYP2C9 gene.

Analysis method 
Warfarin genotyping is performed by amplification of the targeted regions of CYP2C9 and VKORC1 gene by polymerase chain reaction (PCR). Sequencing reaction is carried out by BigDye terminator cycle sequencing kit. Analysis is performed by capillary electrophoresis on 3500 Genetic Analyzer.

Sample requirement 
3.0 mL blood collected in EDTA tube

Preparation 
No preparation required

Instrument platform 
3500 Genetic Analyzer (Applied Biosystems, USA)