Hypercoagulability

Overview of Hypercoagulability Assessment

• Definition: Laboratory testing performed to identify inherited and acquired factors that increase the risk of thrombosis (blood clots)
• Purpose:
  • Evaluate patients with:
    • Unexplained venous thromboembolism (VTE): Deep vein thrombosis (DVT) and pulmonary embolism (PE)
    • Arterial thrombosis in young individuals or at unusual sites
    • Recurrent thrombosis
    • Family history of thrombosis
    • Recurrent pregnancy loss
  • Guide management decisions regarding anticoagulation therapy
• Key Considerations:
  • Testing is not indicated for all patients with thrombosis
  • The decision to perform thrombophilia testing should be based on clinical judgment and consideration of the patient’s risk factors
  • Testing should generally be performed after an acute thrombotic event has resolved and the patient is not on anticoagulant therapy (or after anticoagulation has been discontinued for several weeks), as anticoagulants can interfere with the results

Assays for Assessing Hypercoagulability

These tests evaluate the function or levels of various components of the coagulation system

• Lupus Anticoagulant (LA) Testing:

  • Principle: A series of phospholipid-dependent coagulation assays that detect the presence of lupus anticoagulants (LA), which are autoantibodies that interfere with phospholipid-dependent coagulation reactions in vitro

• Protein C Activity Assay:

  • Principle: Measures the activity of protein C, a vitamin K-dependent anticoagulant protein
    • Protein C is activated by the thrombin-thrombomodulin complex on endothelial cells
    • Activated protein C (APC), along with its cofactor protein S, inactivates Factors Va and VIIIa, inhibiting thrombin generation

• Protein S Activity and Antigen Assays:

  • Principle: Measures the activity and amount of protein S, a cofactor for activated protein C
    • Protein S exists in two forms in plasma:
      • Free Protein S: The active form that acts as a cofactor for APC
      • Bound Protein S: Bound to C4b-binding protein

• Antithrombin Activity and Antigen Assays:

  • Principle: Measures the activity and amount of antithrombin (AT), a natural anticoagulant that inhibits thrombin and other coagulation factors

Molecular Testing for Inherited Thrombophilias

• Factor V Leiden Mutation Analysis:

  • Principle: Detects the presence of the Factor V Leiden mutation (R506Q) in the F5 gene

• Prothrombin G20210A Mutation Analysis:

  • Principle: Detects the presence of the prothrombin G20210A mutation in the F2 gene

Considerations for Testing and Interpretation

• Clinical Context: Interpret test results in the context of the patient’s clinical history, medication use, and other laboratory findings
• Testing Timing: Perform thrombophilia testing when the patient is not acutely thrombotic and is not on anticoagulant therapy (or after anticoagulation has been discontinued for several weeks)
• Sequential Testing: Follow a logical testing algorithm to evaluate for thrombophilia
• Repeat Testing: Repeat positive results for antiphospholipid antibodies (LA, aCL, anti-β2GPI) at least 12 weeks apart to confirm persistence
• Heterozygous vs. Homozygous: A test that can help distinguish between heterozygous and homozygous mutations, but it is not required.
• Reference Ranges: Use appropriate reference ranges for the patient’s age and sex
• Quality Control: Follow established laboratory procedures and quality control guidelines

Algorithm for Thrombophilia Testing

(This is a general guideline. Always follow your laboratory’s specific protocol)

1. Clinical Suspicion of Thrombophilia
2. Initial Testing:
   • PT and aPTT (to screen for coagulation abnormalities)
   • Platelet Count
3. If aPTT is Prolonged, Consider Lupus Anticoagulant Testing
4. If Thrombophilia Testing is Warranted (and Patient is Not Acutely Thrombotic or Anticoagulated):
   • Factor V Leiden Mutation Analysis
   • Prothrombin G20210A Mutation Analysis
   • Protein C Activity and Antigen Assays
   • Free Protein S Antigen and Total Protein S Antigen Assays
   • Antithrombin Activity and Antigen Assays
   • Antiphospholipid Antibody Testing (LA, aCL, anti-β2GPI)
5. Interpret Results:
   • Interpret the results in the context of the patient’s clinical presentation and other laboratory findings
   • Refer to a hematologist or thrombosis specialist for further evaluation and management

Key Terms

• Hypercoagulable State (Thrombophilia): A condition with an increased risk of thrombosis
• Factor V Leiden: A common genetic mutation that causes resistance to activated protein C
• Prothrombin G20210A Mutation: A genetic mutation that leads to increased prothrombin levels
• Protein C: A vitamin K-dependent anticoagulant protein
• Protein S: A cofactor for activated protein C
• Antithrombin: A serine protease inhibitor that inhibits thrombin and other coagulation factors
• Antiphospholipid Syndrome (APS): An autoimmune disorder characterized by thrombosis, pregnancy morbidity, and antiphospholipid antibodies
• Lupus Anticoagulant (LA): An antibody that interferes with phospholipid-dependent coagulation assays
• Thrombosis: Formation of a blood clot inside a blood vessel