How does primary haemostasis work?
- Injury causes vessels to constrict to reduce blood flow, mediated by endothelin - Biochemistry of vessel walls change and negatively charged platelets are attracted to the damaged surfaces - Platelets adhere to exposed collagen via vWF - vWF combines with platelet surface receptor glycoprotein 1B9 and links platelet to collagen - GP6 binds as well leading to further platelet activation - Activation causes platelets to release granule contents (ADP and thromboxane) enhancing the effect - Binding of GP6 to collagen activated GPIIb/IIIa which binds to fibrinogen, acting as a bridge between platelets
How is primary haemostasis assessed?
- Bleeding time - FBC (platelet count) - Platelet function
How is secondary haemostasis assessed?
- PT (stimulates activation via extrinsic pathway) - aPTT (stimulates activation via intrinsic pathway) - TCT (conversion of fibrinogen to fibrin)
What is DIC?
- Process involves systemic activation of coagulation leading to intravascular deposition of fibrin and thrombosis as well as depletion of platelets and coagulation factors - Causes include sepsis, malignancy, massive haemorrhage, severe trauma and pregnancy complications
What is Haemophilia A?
- Factor VIII deficiency - X-linked inheritance - Prolonged aPTT - Treated with desmopressin
What is Von Willebrand disease?
- AD with variable penetrance - Mucosal type bleeding pattern - Reduced vWF +/- reduced platelet aggregation +/- reduced VIII
What is Lupus anticoagulant?
- Phospholipid dependent antibody - aPTT prolonged
What is antiphospholipid syndrome?
- Disrupts annexin V shield - Exposes excess phospholipid
What is thrombophilia?
- Inherited - Deficiencies of natural anticoagulants (antithrombin, Protein C, Protein S)
How does secondary haemostasis work?