LabMed

Prothrombin 20210 Mutation

At a Glance

The prothrombin 20210 mutation is an inherited venous thrombotic disorder. A history of unexplained venous thrombosis in a patient younger than 50 years of age with a family history of venous thrombosis should prompt consideration of the prothrombin 20210 mutation. First, venous thrombosis with heterozygous prothrombin 20210 mutation typically occurs in otherwise healthy individuals at around 40 years of age. Thrombosis may be triggered by surgery, trauma, pregnancy, or prolonged immobilization, such as car or plane rides longer than 8 hours. Venous thrombosis associated with prothrombin 20210 mutation may occur in unusual locations, such as the portal vein, mesenteric vein, superior sagittal sinus, or arm veins, and in multiple veins simultaneously. Any of these indicators of unusual venous thrombosis should prompt consideration of the prothrombin 20210 mutation

The prothrombin 20210 mutation occurs in about 2% of Caucasians, but is rare in individuals of African, Hispanic, or Asian descent. Patients with the prothrombin 20210 mutation are typically heterozygotes with one normal and one abnormal prothrombin gene, resulting in an autosomal dominant heredity pattern (male and female, each generation showing disorder). Homozygous prothrombin 20210 mutations are rare. The prothrombin 20210 mutation results in increased levels of prothrombin in blood.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The primary test to detect the prothrombin 20210 mutation is DNA analysis. Prothrombin 20210 mutation DNA assays can determine whether the individual has two normal prothrombin genes, is heterozygous for the prothrombin 20210 mutation, or is homozygous for the mutation.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Rare individuals have mutations of their prothrombin gene that are different than the prothrombin 20210 mutation (e.g., prothrombin C20209T mutation). Most prothrombin 20210 mutation DNA assays will not detect these mutations, but they are rare, and their association with thrombotic risk is less well established than the prothrombin 20210 mutation.

The majority of plasma prothrombin is made in the liver. Most genetic tests for prothrombin 20210 mutation evaluate DNA purified from white blood cells. Patients with bone marrow or liver transplants may show discrepancies between the prothrombin gene evaluated in white cell DNA and the prothrombin in plasma produced by the liver. In bone marrow transplant patients, buccal swabs can be used for DNA analysis.

What Lab Results Are Absolutely Confirmatory?

DNA-based testing for the prothrombin 20210 mutation is definitive if the patient has not had a liver or bone marrow transplant.

Does the Prothrombin 20210 Mutation Predict Initial or Recurrent Venous Thrombosis or Change Recommendations for Antithrombotic Therapy?

Patients heterozygous for the prothrombin 20210 mutation have approximately a two- to five-fold increased risk of developing venous thrombosis, compared to individuals without inherited thrombophilia, and tend to develop venous thrombosis at a younger age. Most individuals with the prothrombin 20210 mutation, however, never develop venous thrombosis. The risk associated with homozygous prothrombin 20210 mutation has not been determined because of the rarity of the condition. The prothrombin 20210 mutation is associated with an increased risk of fetal loss and venous thrombosis during pregnancy. Testing for the prothrombin 20210 mutation does not, in practice, identify individuals who will definitely develop recurrent venous thrombosis, reduce the incidence of recurrent venous thrombosis, or alter antithrombotic therapy in most cases.

Because the prevalence of prothrombin 20210 mutation is so high in Caucasians, coinheritance with other inherited and acquired thrombotic risk factors must be considered when evaluating patients with a strong family history of venous thrombosis. Multiple risk factors tend to increase the overall risk of venous thrombosis. For example, the prothrombin 20210 mutation and oral contraceptive use together has a higher risk of venous thrombosis than either alone.

Additional Issues of Clinical Importance

The prothrombin 20210 mutation is generally not associated with an increased risk of thrombosis in children prior to puberty, unless they also have other risk factors for venous thrombosis, such as cancer, infection, or intravascular catheters.

The association between the prothrombin 20210 mutation and arterial thrombosis is weak, is controversial, and has no therapeutic implications at present.

Errors in Test Selection and Interpretation

Common errors include ordering a “prothrombin activity,” rather than a prothrombin 20210 mutation DNA assay.

Patients with bone marrow or liver transplants may show discrepancies between the prothrombin gene evaluated in white cell DNA and the prothrombin in plasma produced by the liver. In bone marrow transplant patients, buccal swabs can be used for DNA analysis.

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