Introduction
Recently, much media attention has been focused on genetic testing as a means to determine the appropriate warfarin dosage for an individual patient, thereby substantially reducing the risk of bleeding or clotting events. At the Anticoagulation Forum National Conference on Anticoagulation Therapy held in Chicago in May 2007, genetic testing for warfarin dosing was a hot topic. Even the United States Food and Drug Administration (FDA) has weighed in on this issue. In addition, the American Enterprise Institute-Brookings Joint Center (with input from the FDA) has published a document that reached some very impressive conclusions. Specifically, the report concludes, "We estimate that formally integrating genetic testing into routine warfarin therapy could allow American warfarin users to avoid 85,000 serious bleeding events and 17,000 strokes annually. We estimate the reduced health care spending from integrating genetic testing into warfarin therapy to be $1.1 billion annually, with a range of about $100 million to $2 billion."
So, what's the story? Can genetic testing be used to determine the right warfarin dosage? Does such an approach reduce clinical complications and save the health care industry billions of dollars annually? The answer, quite simply, is maybe, but no one knows for sure. Although the concept may be attractive and this evolving area needs to be researched, good clinical data to support the use of genetic testing for warfarin dosing are not yet available. Also, it is important to realize that the impressive conclusions from the Brookings report mentioned above are based on supposition and projections, not on solid clinical outcome data. Furthermore, some experienced clinicians question whether genetic testing adds significantly to the information one may discern by carefully monitoring the inter-national normalized ratio (INR) and by taking into consideration the numerous patient-specific factors that influence warfarin dosing requirements, such as age, underlying disease states, and concomitant drugs.