Considerations based on your test result.
Despite its widespread clinical use, warfarin (Coumadin®) dosing has remained problematic. It has a narrow therapeutic range, and dosing of warfarin needs to be carefully adjusted to be both safe and effective. Too much can cause adverse bleeding events while insufficient dosing leaves patients at risk of thrombosis, both of which may be fatal.
If you are taking or planning to take warfarin, your physician will have your blood clotting time checked. This involves drawing and testing a sample of blood for prothrombin clotting time, which is expressed as international normalized ratio (INR). Typically, an INR of 2.0-3.0 is desired, and your physician will adjust your warfarin dose up or down to keep the INR in this range.
There is considerable variability in response to warfarin, and different people require different doses to achieve the desired INR. A number of factors affect variability in response to warfarin. These include age, height, weight, sex, ethnicity and other concomitant medications. These factors are usually considered by the physician when starting a patient on warfarin.
However, it is now known that about 40-50% of the variability in response to warfarin is genetic. This prompted the U.S. Food and Drug Administration (FDA) in 2007 to add a black box warning to the label alerting physicians to the genetic effects on warfarin response 1. In 2010, the FDA issued an additional label change to include the expected stable maintenance dose based on CYP2C9 and VKORC1genotype 2. The Genomic Express Warfarin Sensitivity genetic test will provide precisely this genotype information for you. Your physician can then utilize this information to more safely prescribe your warfarin treatment.
The AEI Brookings Institute concluded that if this patient genotype information was routinely utilized in warfarin dosing, it would prevent 85,000 serious bleeding events and 15,000 strokes per year 3. It was further estimated that the healthcare cost savings would be $1.1 billion.
Now, with genetic testing, you have a new tool to make warfarin dosing safer, less costly and provide more effective anti-thrombotic therapy. Ask your doctor today about genetic testing for warfarin sensitivity. Start your treatment utilizing all the information available in order to be both safe and effective.
3 Andrew McWilliam, Randall Lutter, Clark Nardinelli. Health care savings from personalized medicine using genetic testing: the case of warfarin. Working Paper 06-23, AEI-Brookings Joint Center for Regulatory Studies. 2006 [cited 2008 Nov 21].