The Test Sample
What is being tested?
Factor V Leiden and prothrombin 20210 (PT 20210) are genetic mutations that are associated with an increased risk of developing inappropriate blood clots. Two separate tests for these mutations are often performed together to detect the mutations and help determine if an individual has an inherited risk for excessive clotting.
Factor V and prothrombin are coagulation factors, two of a group of proteins essential for proper blood clot formation. When an injury occurs and bleeding starts, a process called hemostasis begins to form a plug at the injury site to help stop the bleeding. Blood cells called platelets adhere to and aggregate at the injury site, and a coagulation cascade begins to activate coagulation factors in sequence. Eventually, a blood clot forms. Once the area has healed, the blood clot dissolves.
There must be an adequate number of each of the coagulation factors, and each must function normally in order for a stable blood clot to form and then dissolve when no longer needed. Too little of the factors, or ones that are dysfunctional, can lead to bleeding or inappropriate clotting (thrombosis).
Factor V Leiden and PT 20210 are two mutations that individuals may inherit from their parents that may cause an increased risk of excessive clotting. A person may inherit one mutated gene copy and be heterozygous or may inherit two mutated gene copies and be homozygous. This may determine to what extent the person is affected.
- During hemostasis, factor V is normally inactivated by a protein called activated protein C (APC) to prevent the blood clot from growing too large. But a Factor V Leiden genetic mutation can lead to an altered factor V protein that resists inactivation by APC. The result is that clotting remains more active than usual, increasing risks of a blood clot forming in the deep veins of legs (DVT) or breaking off and blocking a vein (venous thromboembolism or VTE).
Factor V Leiden mutation is the most common inherited predisposition to abnormal clotting in the United States and it is most common in the Caucasian population. Between 3 and 8 percent of U.S. Caucasians carry one copy of the factor V Leiden mutation and about 1 in 5,000 people have two copies of the mutation. While homozygous cases of Factor V Leiden are more rare, they also carry a higher risk of thrombosis. People with two copies of the mutation may have up to 80 times the risk of thrombophilia while those with one copy have 4 to 8 times the risk, compared to those who do not carry the mutation.
- During normal blood clotting, an enzyme splits prothrombin to form thrombin. A mutation in the gene that codes for prothrombin called prothrombin 20210 can lead to increased amount of prothrombin, abnormal clotting, and an increased risk of a DVT or VTE.
A person with a PT 20210 mutation may be heterozygous or homozygous, although it is very rare to find individuals who are homozygous. The affected heterozygous person will have a mild to moderate increase in their thrombin production, which is associated with 2.5 to 3 fold greater risk of developing a VTE in Caucasians; there is not enough information about risk in those who are homozygous. Although PT 20210 is less common in the U.S. 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.
These mutations are independent and are tested separately, but the tests are often performed at the same time as part of the investigation of a blood clot (thrombotic episode) in someone who is suspected of having an inherited risk factor for an excessive clotting (hypercoagulable) disorder. Each test is used to identify whether or not the specific mutation is present and to determine whether the person has one copy (heterozygous) or two copies (homozygous) of 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.