No Proof Found That Genetic Testing Helps Prevent Blood Clots

Main Category: Vascular
Also Included In: Cardiovascular / Cardiology;  Genetics;  Clinical Trials / Drug Trials
Article Date: 19 Jun 2009 - 3:00 PDT

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According to a new report by HHS' Agency for Healthcare Research and Quality, there is insufficient evidence to conclude that genetic testing for two gene mutations in adults with a history of blood clots helps to prevent a condition known as deep-vein thrombosis or to improve other clinical outcomes.

The report, a summary of which will be published in the June 17 issue of JAMA, also failed to find any benefit from genetic testing of family members of patients who have at least one of the two mutations known as Factor V Leiden (FVL) and prothrombin G20210A as well as a history of deep-vein thrombosis.

As many as 600,000 Americans each year may have deep-vein thrombosis blood clots that form in the legs or pelvis. The condition occurs most commonly in people who are sedentary for a long period of time, such as when recovering from surgery or traveling long distances. The true number of people who develop a pulmonary embolism is unknown, but AHRQ data for hospital patients show that 258,000 individuals were diagnosed with the condition in 2006, and 20,000 died as a result.

"While genetic testing shows great promise to improve treatment and prevent disease, this report clearly shows that we need more research and evidence to achieve its full potential," said AHRQ Director Carolyn M. Clancy, M.D. "But people can help reduce their likelihood of developing a blood clot by talking with their doctor about precautions."

The evidence report was requested and supported by the Office of Public Health Genomics (OPHG) at HHS' Centers for Disease Control and Prevention. The Evaluation of Genomic Applications in Practice and Prevention (EGAPP) Working Group, established by OPHG in 2005, will use this evidence report and other evidence to make recommendations on the validity and utility of genetic tests for FVL and prothrombin G20210A. This report, titled Outcomes of Genetic Testing in Adults with a History of Venous Thromboembolism, is the fifth evidence report requested for EGAPP.

The authors, who were led by Jodi Segal, M.D., of the AHRQ-supported Johns Hopkins Evidence-based Practice Center in Baltimore, failed to find any studies that directly addressed the effect of genetic testing on patient outcomes, but they found research indicating that keeping patients who have a genetic tendency to develop blood clots on blood-thinning drugs such as warfarin reduces the chance of a future clot. This benefit appears to be similar to that seen in patients who do not have the genetic tendency to develop blood clots but who have a history of clots.

The authors also reviewed the evidence for the accuracy of the testing methods used to identify the FVL and prothrombin G20210A mutations, which can signal continued risk of blood clots. The evidence shows that tests for identifying the mutations have excellent analytic validity and that nearly all laboratories report accurate results.

The authors called for randomized trials with sufficiently large sample sizes and long-term follow-up, as well as other research to determine whether changing provider practice based on genetic test results improves patient outcomes.

Source: Agency for Healthcare Research and Quality

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