Research Activities, October 2009: Outcomes/Effectiveness Research: Genetic testing is of unproven value for preventing blood clots

Outcomes/Effectiveness Research
Genetic testing is of unproven value for preventing blood clots

As many as 600,000 Americans each year suffer from venous thromboembolism (VTE), a blood clot in the veins of the body, most often experienced as deep vein thrombosis in the leg or pelvic veins. Pulmonary embolism is the main life-threatening complication of deep vein thrombosis, in which a portion of the blood clot is carried to the lungs, where it can be deadly. The duration of treatment depends on whether the patient is considered to have continuing risk factors for a recurrent VTE. Physicians sometimes recommend that adult patients who are either at high risk for or have had VTE undergo genetic testing to determine if they have genetic mutations that make them especially likely to develop VTE. However, a new study finds there is not enough evidence to prove that genetic testing for two gene mutations in patients with a history of blood clots helps in managing VTE.

Jodi B. Segal, M.D., M.P.H., of the AHRQ-supported Johns Hopkins Evidence-based Practice Center in Baltimore and colleagues reviewed 124 studies addressing genetic testing for two mutations, Factor V Leiden and prothrombin G20210A, associated with VTE. They found that patients with the Factor V Leiden mutation are at a higher risk of recurrent VTEs compared with patients who suffered a VTE and did not have the mutation. Although tests for identifying the mutations have excellent analytic validity and most laboratories report accurate results, studies have not shown whether testing improves outcomes for adults or their family members.

Keeping patients who have a genetic tendency to develop blood clots on blood-thinning drugs (anticoagulants) does appear to reduce the chance of developing future clots. However, 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. This study was funded in part by the Agency for Healthcare Research and Quality (Contract No. 290-02-0018).

See "Predictive value of Factor V Leiden and prothrombin G20210A in adults with venous thromboembolism and in family members of those with a mutation: A systematic review," by Dr. Segal, Daniel J. Brotman, M.D., Alejandro J. Necochea, M.D., M.P.H., and others in the June 17, 2009 Journal of the American Medical Association 301(23), pp. 2472-2485.


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Research Activities, October 2009: Outcomes/Effectiveness Research: Genetic testing is of unproven value for preventing blood clots