TUESDAY, Jan. 20 (HealthDay News) -- Genetic testing isn't cost-effective in guiding initial dosing of the blood thinner warfarin in patients with atrial fibrillation (a type of abnormal heart rhythm), a University of Cincinnati study finds.

Warfarin is used to prevent blood clotting in these patients. In 2007, the U.S. Food and Drug Administration changed the labeling for warfarin to suggest that doctors consider genetic testing before using the blood thinner.

"There are certain genes that are known to contribute to an increased sensitivity to warfarin," study lead investigator Dr. Mark Eckman, professor of medicine, explained in a UC news release.

"The idea behind genetic testing -- also known as pharmacogenetic-guided dosing -- is to help guide the initial, and possibly lower, dose of warfarin for patients," Eckman said. "The hope is that more accurate dosing will translate into decreased major bleeds during the initiation phase of warfarin dosing, which is the first month or so."

He and his colleagues analyzed the findings of three published studies and then created a model to estimate the cost-effectiveness of genetic testing.

They found that genotype-guided dosing did result in better patient outcomes but at a cost of more than $170,000 per quality-adjusted life year gained. They also found that there is only a 10 percent chance that genotype-guided dosing is likely to be cost-effective. The findings were published in the Jan. 20 issue of the journal Annals of Internal Medicine.

The researchers concluded that genotype-guiding dosing is cost effective if it:

• is used for patients at high risk for hemorrhage;
• prevents more than 32 percent of major bleeding events;
• is available within 24 hours;
• costs less than $200.

"This could be accomplished if testing were done in-house, at lower cost and without delays," said Eckman. Currently, most of these tests have to be sent to outside laboratories, which can lead to increased cost and treatment delays.

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