Prothrombin is the precursor of the serine protease thrombin, a key enzyme in the processes of hemostasis and thrombosis. Decreased levels of prothrombin are associated with an increased risk for hemorrhage, whereas elevated prothrombin levels have been associated with an increased risk for venous thrombosis.

Recently a genetic polymorphism located in the 3’-untranslated region of the prothrombin gene has been described. The polymorphism has been associated with increased prothrombin levels as well as an increased risk for venous thrombosis. The polymorphism is due to a single base pair substitution at position 20210 of a guanine (G) for an adenine (A) nucleotide. The mechanism whereby this polymorphism results in increased levels of prothrombin is unknown.

The prevalence of this polymorphism ranges from 1% to 3% in Caucasian populations, but is very uncommon in individuals from Asian or African descent. In contrast, several studies have reported that between 5% to 18% of patients with venous thrombosis have this polymorphism. Furthermore, this polymorphism is not infrequently encountered in patients with an additional hypercoagulable state, especially factor V Leiden and/or thermolabile polymorphism in the methylenetetrahydrofolate reductase (MTHFR).

• The increased risk of venous thrombosis in patients who are heterzygous for the prothrombin (G20210A) gene polymorphism is 3-fold.
• Homozygotes for this polymorphism have been described but are very uncommon.
• Patients with a previous, or current, thrombotic event that have the prothrombin (G20210A) gene polymorphism are potentially at increased risk for recurrence.
• Patients with the prothrombin (20210) mutation are at increased risk of thrombosis when exposed to other risk factors such as: (1) smoking, (2) pregnancy, (3) Obesity, (4) Oral Contraceptives, and (4) Immobility.
• The risk of thrombosis is substantially increased for patients with multiple genetic risk factors (i.e. The "double hit hypothesis") including the Prothrombin (20210) gene mutation, factor V Leiden mutation, hyperhomocysteinemia, methylenetetrahydrofolate reductase (MTHFR) thermolabile polymorphism, protein C deficiency, protein S deficiency and antiphospholipid antibody syndrome(s).
• Definition and confirmation of the Prothrombin (G20210A) gene polymorphism is necessary for genetic counseling of patients for themselves and family members.

This assay utilizes genomic DNA isolated from the buffy coat to determine the genotype of the patient. The PCR products have a restriction site that is created by introducing a nucleotide substitution with a mutant oligonucleotide during amplification. The mutant oligonucleotide was designed with a nucleotide substitution close to the 3' end, such that the combination of the nucleotide substitution and the genetic abnormality created a new restriction enzyme cleavage site. The new restriction site for HindIII is thus introduced in the amplified fragments. The DNA is then analyzed by agarose gel electrophoreses and compared to restricted samples from a normal individual and an individual who is heterozygous for the prothrombin (20210) gene mutation.

CPT Codes: 83890, 83892, 83894, 83898, 83192

Prothrombin (20210) Gene Mutation:

Specimen Requirements: Whole Blood (EDTA or 3.2% Sodium Citrate)

Transport temperature: Ambient (22 - 24° C)

Specimen Stability: 7 days at 22 - 24° C

Assay Setup days: Tuesday

Assay Time: 2-4 days

Report Turn-around-Time: 1 week (via Fax)

Note: It is recommended that a separate plasma sample be sent to correlate the PTG 20210 DNA analysis with a Factor II (functional or antigenic) level obtained at the same collection time. The specimen requirements and shipping instructions for the Factor II assays are as follows:

Factor II Assay, Functional or Prothrombin (FII) Antigen:

Specimen Requirements: Plasma (3.2% Sodium Citrate)

Transport temperature: Frozen (-20 to -80° C)

Specimen Stability: 6 months at -20 to -80° C

Assay Setup days: Factor II Assay- every day; FII Ag – Wednesday

Assay Time: 4-24 hours

Report Turn-around-Time: 1 week (via Fax)

Call (800) 441-1416 or (919) 684-6366 to request shipping instructions, test requisitions, collection requirements, and additional information.

Activated Protein C Resistance (APC) aPTT-Based

Activated Protein C Resistance (APC) PT-Based

Anticardiolipin Antibodies (IgG, IgM, IgA)

Antithrombin III Activity

Factor II Assay (Functional)

Factor V Leiden Mutation (FV:^R506Q)

Lupus Anticoagulant Panel

Methylenetetrahydrofolate Reductase (MTHFR) Mutation

Plasminogen Activity

Protein C Functional Assay

Protein S Functional Assay

Prothrombin (Factor II) Antigen

Thrombosis Panel

 

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Last Modified: May 8, 2000