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Washington University offers strong recap of study using genetic testing to determine safe dosing of warfarin

Genetic testing helps set safe dose of common blood thinner

Our Review Summary

This news release describes results of a study designed to learn whether testing for the presence of three gene variants could make dosing with the blood thinner warfarin safer for patients given the drug to prevent blood clots after joint replacement surgery.

The study found a modest reduction in the risk of bleeding or clots (from over- or under-dosing) in those whose regimens were developed in part by genetic testing for the variants, compared to those whose doses were calculated without the genetic testing.

The release does an overall good job in describing the study, its purpose and design; and in quantifying the results. It could have been even stronger if it had included more information about newer alternatives to warfarin that are growing in use and an explicit statement that no one is yet recommending routine genetic testing for the variants based on this study. And although the headline somewhat over promises clinical benefit at this point in time, thoughtful readers will come away with a decent understanding of the context of the research and its potential impact.


Why This Matters

Some estimates put the number of Americans regularly taking the clot-preventing blood thinner warfarin and several newer anticoagulants at more than six million. Warfarin (sold under the brand name Coumadin) requires frequent blood testing to address risks of overdoses (and potentially lethal bleeding) and under-dosing (ineffective prevention of strokes and other blood clots). Because warfarin is cheap, and its effects are reversible with vitamin K, research designed to make it easier and safer for patients to take is likely to be highly newsworthy for them and their caregivers.


Does the news release adequately discuss the costs of the intervention?


Although the release doesn’t give actual costs of warfarin versus some of the newer drugs, or factor in the cost of the usual monthly blood testing required of those taking the drug, it does note the cost of the gene testing used for the study, and that the $200 price tag is now less than a month’s prescription of one of the newer anti-coagulants on the market.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?


The release gives results in both actual numbers of patients and the percentage of reduction of adverse events in those given the genetic test and a comparison group.

Does the news release adequately explain/quantify the harms of the intervention?


Although it does so in general terms, the release covers the essentials: the risk of using blood thinners like warfarin and the risks of not using them.

Does the news release seem to grasp the quality of the evidence?


The release offers a good description of the design of the study. It was randomized and enrolled more than 1,600 older patients at high risk of blood clots following surgeries. The release explains that one group received warfarin dosing based on standard factors (age, height and weight) and the second group was dosed using these clinical factors plus their genetic variants.

The release also offers a detailed breakdown on how many fewer side effects occurred among patients had genetic testing completed compared to those who didn’t.

Does the news release commit disease-mongering?


No mongering here.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

Although the release briefly mentions the availability of a “newer anticoagulant,” it should have included a sentence or two about these newer injectable drugs and their overall risks and benefits in comparison to warfarin. It would also have been helpful to tell readers whether the genetic testing that appears to play a role in safer warfarin dosing would have clinical relevance for informing the use of the new blood thinners as well.

The fact is that genetic testing is irrelevant for the newer anti-coagulants because they operate in a completely different manner. But all the blood thinners — old and new — carry the same risk of bleeding. The problem with warfarin is the variability in blood levels which requires frequent monitoring, hence the genetic tests to guide dosing.

Does the news release establish the availability of the treatment/test/product/procedure?

Not Satisfactory

The careful reader will get it: testing for these genetic variants is still an experimental practice for the most part, and further testing of how the mutations affect warfarin is needed. But the release could have been more explicit in saying that no one is yet recommending genetic testing for millions of warfarin users.

While the genetic tests are “available” in the sense that anyone can order them for the most part, they are not routinely used clinically and probably wouldn’t be covered by insurance so in that sense they are not widely available to most people.

Does the news release establish the true novelty of the approach?


The release describes how the genetic test used in the new study differs from previous similar studies.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?


Overall the language is careful and contextual. The headline should have been toned back a bit to note that this is early research and more study is needed before concluding that “Genetic testing helps set safe dose of common blood thinner,” as the headline now states.

Total Score: 8 of 10 Satisfactory


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