Inherited and Acquired Thrombophilia Flashcards
What is thrombophilia?
Thrombophilia is a term describing inherited or acquired defects of haemostasis leading to a predisposition to venous or arterial thrombosis.
What is part of the thrombophilia screen?
- PT, APTT
- Fibrinogen
- Lupus Anticoagulant
- Anti-cardiolipin antibodies
- Antithrombin activity
- Protein C activity
- Free protein S antigen
- Factor VII activity
- Activated Protein C Resistance Factor V Leiden genotype
- Prothrombin genotype
Why is pregnancy a hypercoagulable state?
- Resistance to activated protein C
- Protein S activity decreases
- Fibrinogen and Factors II, VII, VIII, X increases
- Levels and activity of fibrinolytic inhibitors increase
What are the main inherited thrombophilias?
- Activated protein C resistance/Factor V Leiden
- Protein C and S deficiency
- Antithrombin deficiency
- Prothrombin variant
What is Factor V Leiden?
Activated protein C resistance
Factor V Leiden differs from normal factor V by a single nucleotide substitution (Arg506Gln). This variation makes factor V less likely to be cleaved by activated protein C. As factor V is a cofactor for thrombin generation impaired inactivation by activated protein C results in a tendency to thrombosis.
How much does the thrombotic risk increase in someone with Factor V Leiden who is on oral contraceptive pill?
35-fold increase
How much does the thrombotic risk increase in someone with Factor V Leiden who is on oral contraceptive pill?
35-fold increase
What is a prothrombin variant?
A mutation in the 3′ untranslated region of the prothrombin gene, which is associated with elevated levels of prothrombin and a 2–3-fold increase in the risk of venous thrombosis. There is also down-regulation of fibrinolysis, due to thrombin activated fibrinolysis inhibitor
How is factor V Leiden inherited?
Autosomal dominant inheritence
What is Protein C/Protein S deficiency?
These vitamin K-dependent factors act together to cleave and neutralize factors V and VIII. Heterozygote deficiency for either protein risk thrombosis
How is protein C and S deficiency inherited?
Autosomal dominant
Where are protein C and S synthesised?
Liver
What are acquired causes of protein C or S deficiency?
- Liver disease
- Severe infection/septic shock/DIC
- Postoperative state
- Pregnancy/OCP
- Acute thromboembolic disease
- Nephrotic syndrome
What is Antithrombin III deficiency?
Antithrombin is a co-factor of heparin, and inhibits thrombin. Deficiency leads to uninhibited thrombin production. Recurrent thrombotic episodes occur starting at a young age in the inherited variety. Patients may be relatively resistant to heparin as antithrombin is required for its action.
What are those with Antithrombin III deficiency resistant to?
Heparin - acts using antithrombin