At a Glance
Why Get Tested?
To determine whether you have an inherited gene mutation that increases your risk of developing a venous thromboembolism
When to Get Tested?
When you have had an unexplained thrombotic episode, especially when you are less than 50 years old and have no other risk factors
A blood sample taken from a vein in your arm
Test Preparation Needed?
No test preparation is needed.
The Test Sample
What is being tested?
Factor V and prothrombin are coagulation factors, a group of proteins produced by the liver that is activated in a step-by-step process called the coagulation cascade when a blood vessel is injured. The result of the coagulation cascade is a blood clot that creates a barrier at the injury site, protecting it until it heals.
Factor V Leiden is a variant form of factor V with a genetic point mutation, a change in one of the nucleotides on the gene that codes for the production of factor V protein. This altered protein activates normally, but resists being degraded by activated protein C (APC) during coagulation. The result of this resistance is an increased level of thrombin in the blood and an increased risk of venous thromboembolism (VTE).
Prothrombin (PT) 20210 is a variant form of prothrombin, also caused by a genetic point mutation. PT 20210 is also associated with an increased risk of VTE.
Factor V Leiden mutation is the most common inherited predisposition to abnormal clotting in the United States. Its prevalence is about 5-15% in Caucasian populations. A patient with Factor V Leiden mutation 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 who are heterozygous have a 3 to 8 fold greater risk than normal of developing a VTE, while those who are homozygous have a 50 to 80 fold increased risk of thrombosis.
Similarly, a patient with a single variant gene copy of PT 20210 is heterozygous and with two copies is homozygous. The affected person 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 in the U.K. 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. Patients who are heterozygous for PT 20210 have a 2 to 3 fold increased risk of venous thromboembolism. The risks of having homozygous PT 20210 have not been established.
Factor V Leiden and PT 20210 are independent mutations that are tested separately. The testing of each is intended to identify whether or not the specific mutation is present and to determine whether the person is heterozygous or homozygous for that mutation.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Ask a Laboratory Scientist
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.