A set of common genetic variants accounts for up to 40% of the variance in optimal dosage of warfarin, a common anticoagulant [for review, see Carlquist and Anderson, 2011]. This discovery has garnered much attention, since bleeding complications from warfarin are not rare and can be serious. In 2010, the FDA revised warfarin labeling to include dosage guidelines based on genotype – a first. However, it is not yet clear that the genetic tests bring additional clinical utility beyond what can be done by skillful monitoring of standard blood clotting assays, such as the INR.
