WARFARIN IS AN ANTICOAGULANT THAT IS USED TO PREVENT BLOOD CLOTS FORMING.

  Unfortunately, one size does not fit all when it comes to Warfarin dosing. Some people need a lot of Warfarin to get the desired effect, while others need only a little. Deciding how much each individual patient needs can be difficult to predict and often requires several months of blood testing and dose adjustment. Too much Warfarin can increase the risk of bleeding, whilst too little can lead to blood clot formation. Maintaining the INR (the blood test used to monitor your Warfarin therapy) within your therapeutic range is essential to sustaining Warfarin's effectiveness and safety. A new gene test is now available to assist with this.

What is this new test?

Knowing the genotypes of CYP2C9 and VKORC1 can predict 50-60% of the variation in drug dosage requirements for Warfarin when age and body height are included. Vitamin K Epoxide Reductase complex, subunit 1(VKORC1). VKORC1 is involved in the recirculation of vitamin K which is essential to produce the blood clotting factors. Warfarin acts by reducing the action of VKORC1 which is needed for  the blood clotting factors. This thins the blood and is used to prevent blood clotting. If too much warfarin is taken then the patient is at risk of bleeding. Too little leads to a risk of blood clotting. It usually takes some weeks for the correct dose of warfarin to be found for an individual patient.

The warfarin pharmacogenomic test can help determine the appropriate dose of warfarin for a patient. It has been shown to get a patient to the correct (therapeutic) dose faster with less bleeding episodes.

CYP2C9 is involved in the breakdown of the most active form  of warfarin. By testing these two genes, one can identify people who need less dosage to reach the therapeutic level required. Alternatively if people with variants in these genes are put on normal dosage they bleed more. VKORC1 has been found to have variations in the part of the gene that regulates the amount of VKORC1 made. GenesFX Health does a gene test that shows how much VKORC1 is available. It has been found that about 50% of people have some changes in CYP2C9 or VKORC1 that mean they require a smaller dose of warfarin.

If other factors are taken into account a formula can be used to calculate the recommended starting dose and it acounts for 50-60% of the variation in dosage between different people.

New England Journal of Medicine (NEJM) - This article describes that the best way to work out warfarin dose is to use pharmacogenomic testing and this is better than using clinical information or a fixed dose.www.ncbi.nlm.nih.gov/pubmed/19228618 

What should I do now?

Discuss DNAdose with your doctor to see whether this test is right for you. Download a referral form here

All pharmacogenetic test results are interpreted and reported by clinical geneticists at GenesFX Health.

The GenesFX Health scientific advisory board comprises clinicians, geneticists, pharmacists and clinical pharmacologists.