Tests and diagnosisBy 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 either is done as a secondary test to confirm the results of the APC resistance test or is done alone to determine whether you have a factor V gene mutation. If you're already taking medication for thrombosis, you're likely to have only the genetic test because blood-thinning (anticoagulant) medications interfere with the activated protein C resistance test. The genetic test also can determine whether you've inherited one or two copies of the gene mutation.
Testing babies prenatally or soon after birth isn't recommended, nor is screening of children who don't have symptoms of clotting problems. Because blood clots are so unusual, even in children with factor V Leiden, it's recommended that you wait until your child is an adult who can fully understand the risks and benefits associated with genetic testing.
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