How is it used?
Factor V Leiden and prothrombin 20210 tests are ordered, along with other tests related to , in some circumstances following the diagnosis of venous thromboembolism. The most common reason is to investigate someone who has had a venous thromobosis and is both less than 50 years of age and comes from a family where two or more other family members have been affected. In this situation testing helps in decisions about whether to start anticoagulation therapy and how long it should continue.
Activated protein C (APC) resistance testing is done to screen for Factor V Leiden. About 95% of the time, those who have APC resistance will have a Factor V Leiden . If resistance is present, then a test for the Factor V Leiden gene mutation is done, both to confirm the diagnosis and to determine whether the patient is or for the mutation.
The PT 20210 mutation must be diagnosed with genetic testing, checking directly for the gene mutation, and determining whether the patient is heterozygous or homozygous. Although prothrombin levels are usually moderately elevated with this mutation and could be measured, they are not clinically useful in finding this mutation.
At this time, experts do not recommend screening the general population, testing in unselected patients presenting with venous thrombosis or their family members. If the mutation is present, then the person is at a very small increased risk for developing a blood clot, but there is variability in how the gene is actually expressed. Many of those who do have the mutation(s) will never have a VTE.
When is it requested?
PT 20210 and Factor V Leiden tests are ordered when a patient has a first at a relatively young age (less than 50 years old). In Australia, current expert advice is that testing of family members is rarely useful. Knowledge of whether a patient or family member has a Factor V Leiden or PT 20210 gene mutation very rarely alters the management plan following diagnosis of a venous thromboembolic event and does not change the advice given to a patient regarding the risk of venous thromboembolic events after taking a careful history of previous thrombotic events and relevant family history.
Once APC Resistance testing, Factor V Leiden mutation testing, and PT 20210 gene mutation testing has been done it is usually not repeated unless there is a need for verification.
What does the test result mean?
Resistance to activated Protein C is due to Factor V Leiden 95% of the time, but if resistance is present the Factor V Leiden mutation should be confirmed with genetic testing.
Factor V Leiden is the most common inherited clotting disorder. Its prevalence is increased in those of European descent, being present in about 4% of the Caucasian population. A patient with Factor V Leiden may be heterozygous (has one copy of the changed gene and one normal gene) or homozygous (has two copies of the changed gene, this is more rare). Those that are heterozygous have about a 5-10% greater risk than normal of developing a venous thromboembolism (VTE), while those who are homozygous have a reater risk of thrombosis although this risk is still small.
If you have a single gene copy with the PT 20210 mutation, then you are heterozygous, if both copies are changed, then you are homozygous. Someone with a heterozygous or homozygous PT 20210 mutation will have a mild to moderate increase in their thrombin production, raising their risk of developing a VTE a small but significant amount. Although PT 20210 is less common than Factor V Leiden (about 1-2% of the general population), it is also more prevalent in Caucasians than in those of other ethnic backgrounds.
Is there anything else I should know?
The risks that are associated with Factor V Leiden, PT 20210, and other inherited and acquired factor deficiencies that are thrombophilic (increase the risk of developing blood clots such as protein C and protein S deficiencies) are independent. You can have more than one of them and their associated risks are cumulative. Added to these inherited risks and acquired risks are controllable risk factors, such as oral contraceptive use, that may exacerbate the combined underlying risk factors. For instance, if you are heterozygous for Factor V Leiden, you may be at about a 10% greater than normal risk of developing a VTE. If you use oral contraceptives, that risk can jump to 35% higher than normal.
Factor V Leiden and PT 20210 are genetic tests and as such you should have a detailed discussion with your doctor before agreeing to undertake the test. This discussion should include the reasons why the test is being recommended and how this will affect your medical management now and in the future.