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% of the Caucasian population. 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.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.
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.
