Warfarin is an anticoagulation drug that is used in the prevention of thrombosis. It functions to decrease blood coagulation by inhibiting vitamin K epoxide reductase, thus antagonizing vitamin K1 recycling and subsequently depleting active vitamin K1.

It is commonly applied to prevent or treat various cardiac arrhythmia such as atrial fibrillation as well as pulmonary embolism. Dosing of Warfarin is delicate as its major adverse effect is hemorrhage or bleeding.

This is further complicated by its interaction with many commonly used medications as well as various food products. Hence at the initial stage of a Warfarin treatment, the patient may be subjected to multiple blood testing such that a proper Warfarin dosage can be achieved.

The effectiveness of Warfarin treatment is also affected partially by genetic factors. In particular, pharmacogenomic studies have identified three single nucleotide polymorphisms (SNPs) that are important determinant of the initial Warfarin dosage.

Two of the SNPs are found in the cytochrome P450 enzyme gene CYP2C9 known as CYP2C9*2 (C430T), CYP2C9*3 (A1075C). The third SNP is found in the Vitamin K Epoxide Reductase Complex Subunit 1 (VKORC1) known as VKORC1 (1639G→A).

Several reports suggested that using such genetic information may improve the initial estimate of what is a reasonable warfarin dose for individual patients. For example, mutations of VKORC1 make it less susceptible to suppression by warfarin and hence individuals carrying such mutations may require higher dosage of warfarin.

Principle of the Test and Product Description

Norgen’s Warfarin Genotyping (VKORC1) Kit uses PCR to determine the genotype of a human Vitamin K Epoxide Reductase Complex Subunit 1 (VKORC1) polymorphism (a G→A mutation). First, genomic DNA is isolated from the individual(s).

This can be achieved by using Norgen's Saliva DNA Collection, Preservation and Isolation Kit (Cat# RU35700). The genomic DNA is then subjected to two PCR reactions - one for the detection of normal (Control) version (G) of the locus and one for the detection of the altered (Mutation) version (A).

The products from the two PCR reactions are then resolved and visualized using standard DNA agarose gel electrophoresis. The expected molecular weights of both PCR products are identical, at 377 bp. The presence or absence of the PCR product is then recorded.

The information will then be used to determine the genotype of each individual for VKORC1, with the possibility of being Homozygous Wild Type (PCR product only present in Wild Type reaction), Heterozygous (PCR product present in both reactions) or Homozygous Mutant (PCR product only present in Mutant reaction.