Tests and diagnosis

By Mayo Clinic Staff

Your doctor will likely suspect factor V Leiden if you've had one or more episodes of thrombosis or pregnancy loss or if you have a strong family history of thrombotic disease. Your doctor can confirm that you have factor V Leiden with a blood test. Two types of tests can be done:

  • Activated protein C resistance test. Your blood sample may be tested to determine whether your blood is resistant to activated protein C, one of the anti-clotting proteins that help control factor V. This is known as an activated protein C (APC) resistance assay. If your blood is resistant to activated protein C, you likely have a mutation in the factor V gene.
  • Genetic test. A genetic test is done to determine whether you have a factor V gene mutation. It may also be used to confirm the results of the APC resistance test or to determine whether you've inherited one or two copies of the gene mutation.

    If you're taking blood-thinning medications (anticoagulants), you may have only the genetic test. Anticoagulants interfere with the activated protein C resistance test.

Testing babies before or soon after birth isn't recommended. Children who don't have symptoms of clotting problems also don't need screening. Blood clots are rare, even in children with factor V Leiden. Testing isn't recommended until adulthood.

When your child is an adult, he or she will be better able to fully understand the risks and benefits associated with genetic testing. Chances are good that your child may never have any signs or symptoms related to factor V Leiden.

July 14, 2015