Medicare will not pay for genetic tests to determine best Warfarin dosage, according to proposed decision

CMS will not provide Medicare coverage for a genetic test that physicians can use to determine the proper dosage of the blood thinner drug warfarin, the New York Times reports.

In a proposed decision posted Monday on the agency's Web site, CMS said there is not enough evidence to indicate that such a test offers a better outcome for patients compared with the existing method. As many as one million or more Medicare beneficiaries annually take warfarin.

Physicians currently base the dosage on several factors, including age and weight, and then every few days test whether a patient's blood is clotting properly and adjust the dosage accordingly. According to the Times, finding the best dose of warfarin, known under the brandname Coumadin, is "notoriously tricky." A dosage that is too small could be ineffective at preventing blood clots, while a dosage that is too large could cause internal bleeding. The Times reports that tens of thousands of patients visit hospitals each year because of complications from the drug.

According to the Times, some studies have found that the genetic test, known as a warfarin response test, can help physicians discover the proper dosage more quickly. However, CMS said that there was no evidence that the test would reduce the risk of blood clots or hemorrhages. Conclusions about the benefits to patients "seem to us premature, even though they are intuitively appealing," CMS said. However, the agency said that it will cover the costs for the tests -- typically between $50 and $500 -- as part of clinical trials to determine the test's efficacy.

Reactions from medical societies were divided on the proposed decision, the Times reports. FDA recommends but does not require the genetic test to be conducted before a patient takes warfarin. A month-long public comment period currently is open on CMS' proposed decision (Pollack, New York Times, 5/5).