The mutation renders Factor V insensitive to the anti-coagulant action of activated protein C (APC); this phenomenon is sometimes referred to as "APC resistance".
The presence of one mutated F5 gene increases the risk of venous thrombosis by 3-8 fold and the risk of pregnancy loss by 2-3 fold. There is dispute regarding the clinical utility of this information in an unaffected patient, or in the management of an affected patient. The presence of two mutated F5 genes is associated with a higher risk of venous thrombosis. Other genetic and non-genetic factors contribute to the risk of coagulation, and the test result needs to be considered in the context of the patient’s clinical presentation and family history.
This is an assay for heritable variants which can alter the probability that a person will develop a disorder. The test result is not, in isolation, diagnostic of a disease and the test result is not necessarily clinically significant for the patient's relatives.
Analysis of the F5 gene for the specific Leiden mutation, c.1691G>A. Variants in the FV gene other than Factor V Leiden will not be detected by this test.
Requesting the test
This test can be requested by any medical practitioner.
4 mL blood in EDTA (separate tube required). Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.