Fibrinolytic Disorders

Diagnosis

Indications for Testing

Laboratory Testing

  • Laboratory identification of tPA deficiency is complex due to fluctuation of tPA levels in blood (acute phase reactant), as well as fluctuating levels of PAI-1 (acute phase reactant, diurnal variation), which binds and inactivates tPA
  • Laboratory measurement of PAI-1 must address several issues
    • PAI-1 is an acute phase reactant
    • PAI-1 has diurnal variation, with higher values in the morning and decreased values in the afternoon
    • Identification of PAI-1 deficiency is complex, and values should be interpreted in conjunction with values for tPA
      • Many laboratory assays are designed to identify elevated PAI-1 levels and cannot accurately quantify low values
      • Levels below the limit of quantification may be seen in both PAI-1-deficient patients and in individuals with normal levels
      • Specialized testing may be necessary to definitively diagnose severe PAI-1 deficiency
  • Suspected plasminogen deficiency – order plasminogen activity test
  • Suspected alpha-2-antiplasmin deficiency – order alpha-2-antiplasmin activity test
  • Recurrent deep vein thrombosis in patient with negative workup for common defects – consider genotyping

Differential Diagnosis

Clinical Background

Abnormalities in the fibrinolytic system may be associated with thrombosis or bleeding. Congenital fibrinolytic abnormalities are uncommon; acquired abnormalities are not unusual.

Pathophysiology

  • Formation of a fibrin clot occurs in response to vascular injury
  • Fibrinolytic system breaks down fibrin clot, converting fibrin to soluble degradation products
    • Components of the fibrinolytic system include plasminogen, plasminogen activators, plasminogen activator inhibitors, and alpha-2-antiplasmin  
    • Fibrinolysis is precisely regulated by these activators, inhibitors, and cofactors

Components of Fibrinolytic System

Plasminogen
  • Synthesized in the liver and converted to its active form (plasmin) by plasminogen activators
  • Plasmin degrades fibrin (and fibrinogen), forming soluble fibrin degradation products
  • Excessive plasmin formation may result in increased fibrinolysis and bleeding
  • Deficiency may be inherited or acquired due to disseminated intravascular coagulation, liver disease, or fibrinolytic therapy
    • Inherited plasminogen deficiency is rare, usually autosomal dominant; may be quantitative (type 1) or qualitative (type 2)
      • Incidence – <1/1,000,000
      • Clinical presentation – ligneous conjunctivitis, altered wound healing, or pseudomembrane formation
    • Presence of isolated heterozygous plasminogen deficiency does not appear to increase the risk of thrombosis
      • Thrombotic risks caused by homozygous deficiency remain unclear
Tissue plasminogen activator (tPA)
  • Plasminogen activator is synthesized by endothelial cells and released in response to endothelial cell stimulation
  • tPA converts plasminogen to plasmin, which subsequently degrades fibrin (and fibrinogen), forming soluble fibrin degradation products
    • Low concentrations of circulating tPA are found in the blood
  • Increased tPA may result in increased fibrinolysis and bleeding
  • Deficiency has an uncertain association with thrombosis
Plasminogen activator inhibitor-1 (PAI-1)
  • Released primarily by the liver and adipose tissue
  • Levels are regulated by metabolic factors such as triglycerides, cholesterol and insulin
  • Binds to and inhibits plasminogen activators such as tPA, forming inactive complexes that are cleared by the liver
    • PAI-1 is found in its active form in blood, as well as in an inactive form (primarily in platelets), and in complexes with plasminogen activators
  • Increased PAI-1 levels may be associated with venous or arterial thrombosis, although routine testing of thrombophilic patients for this disorder is not recommended
    • PAI-1 is an acute phase reactant and may be elevated in patients with metabolic syndrome, cancer, surgery, pregnancy, or sepsis or other inflammation
    • PAI-1 has diurnal variation with higher concentration in the morning and decreased concentration in the afternoon
  • Inherited deficiency
    • Rare autosomal recessive disorder
    • Clinical manifestations – associated with moderate to severe bleeding in homozygous individuals (complete deficiency)
      • Bleeding is usually post-traumatic rather than spontaneous
    • Most PAI-1 assays are designed to identify elevated PAI-1 concentrations rather than PAI-1 deficiency
      • Low concentrations may not be accurately quantified
  • Inherited polymorphism – single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the SERPINE1 gene is the major genetic determinant of PAI-1 expression
    • Clinical presentation
      • Individuals with 4G/5G and 4G/4G genotypes, especially those with other thrombophilic risk factors, have increased risk for venous thromboembolism
      • 4G/5G and 4G/4G genotypes are associated with increased risk of myocardial infarction
      • Some studies have associated the 5G/5G genotype with elevated risk of ischemic stroke (IS)
Alpha-2-antiplasmin
  • Secreted by the liver
  • Binds to and inhibits plasmin
    • Contribution of elevated alpha-2-antiplasmin to thrombotic risk has not been reported
  • Inherited deficiency
    • Rare autosomal recessive disorder
    • Clinical presentation
      • Heterozygotes – usually mild mucosal bleeding
      • Homozygotes – may manifest with severe bleeding episodes (may resemble congenital hemophilia)

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Plasminogen Activity 0030190
Method: Chromogenic Assay

Determine plasminogen activity in plasma

Not a first-line test for diagnosing inherited thrombotic or bleeding disorders

Not recommended for patients receiving fibrinolytic inhibitors  
Tissue Plasminogen Activator, Antigen 0099187
Method: Enzyme-Linked Immunosorbent Assay
Determine quantity of tPA in plasma

May be helpful in detecting disorders of the fibrinolytic system

Not a first-line test for diagnosing inherited thrombotic or bleeding disorders

Acute phase reactant

 
Plasminogen Activator Inhibitor 1, Activity 0098781
Method: Bioimmunoassay

Quantify active PAI-1 in human plasma

Assay designed to detect elevated PAI concentrations; low concentrations not accurately quantified

Not a first-line test for diagnosing inherited thrombotic or bleeding disorders

Acute phase reactant

Diurnal variation

 
Alpha-2-Antiplasmin, Activity 0098727
Method: Chromogenic Assay

Determine alpha-2-antiplasmin activity in plasma

Not a first-line test for diagnosing inherited thrombotic or bleeding disorders

   
Plasminogen Activator Inhibitor-1, PAI-1 (SERPINE1) Genotyping 2004980
Method: Polymerase Chain Reaction/Fluorescence Monitoring

Assess genetic susceptibility for VTE or MI in individuals with personal or family history of thrombotic events

Clinical sensitivity – unknown

Variants other than 4G/5G are not evaluated

Diagnostic errors can occur due to rare sequence variations