Contrary to what has been suggested, it appears genetic tests do not help to predict optimal doses of the blood thinner warfarin for patients.
This was the finding of a late-breaking clinical trial whose results were presented at the American Heart Association's Scientific Sessions 2013 in Dallas, TX, recently.
It is important to get the dose of warfarin right for individual patients. If the dose is too high, there is a risk of internal bleeding, and if it is too low, it can lead to potentially life- threatening blood clots.
Patients taking the blood thinner have to be checked regularly to ensure the dose is appropriate.
There have been suggestions that identifying genetic markers in the blood could help to predict the optimal dose for the individual patient so he or she can start on it from the beginning and thus avoid the many changes required.
The genetic test looks for two genes - one that influences how the liver metabolizes warfarin, and the other is about how the body responds to the blood thinner.
The COAG trial found genetic markers did not help
However, the Clarification of Optimal Anticoagulation through Genetics (COAG) trial results did not support this view.
For the trial, which took place between 2009 and 2013, researchers put 1,015 patients required to take warfarin because of a history of stroke, venous thrombosis or atrial fibrillation, into two groups.
With one group, warfarin dosage was determined only from clinical information, such as age, weight and smoking status. For the other group, dosage was based on similar clinical information plus genetic testing.
The randomized, double-blinded, controlled trial took place at several centers, and all patients received an initial dose of warfarin, which was then adjusted 4 to 5 days later according to standard clinical information, with or without genetic testing.
The patients, whose average age was 57, were followed-up for up to 6 months. Of these, 27% were African American, 28% had atrial fibrillation, and 58% had deep vein thrombosis, either in the leg or lung.
But the results showed that having the genetic information made no difference - for both groups, blood thinning was within the desired range 45% of the time for the first 4 weeks.
African Americans fared worse
Moreover, for the African American patients, the ones whose dosage was decided with the help of genetic information did not fare as well as counterparts whose dosage was decided only from the clinical information.
Lead author Dr. Stephen Kimmel, a professor of medicine and epidemiology at the University of Pennsylvania School of Medicine, says the finding shows the value of doing clinical trials for genetic testing:
"There's a lot of debate about when to bring genetics into clinical practice, and whether or not you need clinical trials before widely using genetics. For a drug as complex as warfarin, the COAG trial demonstrates the utility of performing such trials."
A study published in The Lancet in 2011 found that patients who self-monitor their blood thinning therapy can almost halve their risk of thromboembolic events like stroke, deep vein thrombosis and heart attack, compared with patients on traditional care.