Your Resource for all Things Relating to Factor V Leiden

How is Factor V Leiden diagnosed?

Testing for Factor V Leiden is done with a simple blood test. There are two types of tests performed that together determine whether you have Factor V Leiden.

  • First, a blood sample is tested to see if your blood is resistant to activated protein C (one of the proteins that helps control factor V).
  • If your blood is resistant to activated protein C, there is a 90-95% likelihood that you have a mutation in the factor V gene.
  • Second, a genetic test is usually done to confirm the results of the activated protein C test. In this test, the DNA is isolated or separated from blood cells and your factor V gene is examined to see if there is a mutation in your DNA code. If a mutation is found, then you have Factor V Leiden.
  • This second genetic test is considered definitive. This means that approximately 100% of individuals who have the Factor V Leiden mutation will be detected by the genetic test.
  • Since the genetic test examines the actual DNA code, it is able to distinguish heterozygotes (individuals with the mutation in one of the two genes) from homozygotes (individuals with mutations in both of the genes).
  • Sometimes the genetic test is ordered first without ever doing the resistance to activated protein C testing. 

Companies like 23andme and others are now offering DNA genetic testing for Factor V Leiden as part of their product line. This allows you to test for Factor V Leiden at home.


Check out “How Can I Get Tested” for more information about the benefits and concerns of “direct-to-consumer” genetic DNA testing.


If you receive positive results for Factor V Leiden from a home DNA testing kit, we recommend that you contact your healthcare professional and let them know as soon as possible. Together you can review the results and make any changes to your current plan of care.

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