Haemostasis Flashcards
what is haemostasis?
The arrest of bleeding and the maintenance of vascular patency
what are the components of a normal haemostatic system?
Primary Haemstasis - platelet plug
Secondary - fibrin clot
Fibrinolysis
Anticoagulant Defences
what are the three stages of primary haemostasis?
Adhesion
Aggregation
Activation
what occurs in the adhesion stage of primary haemostasis?
Platelets bind to subendothelial collagen via Glycoprotein 1b and Von Willebrand Factor
what occurs in the aggregation stage of primary haemostasis?
Platelets attach to each other via GPIIb/IIIa and fibrinogen.
Activation stage occurs at same time.
what occurs in the activation stage of primary haemostasis?
Aggregation stage occurs at the same time
Platelets alter shape to expose phospholipid for coagulation activation and fibrin production.
Granules further stimulate platelet activation/recruitment eg Thrombin,Thromboxane A2 and ADP via receptors. Positive feedback loop as more platelets stick.
what is the role of the additional chemicals in primary haemostasis?
ADP attracts more platelets, serotonin is a vasoconstrictor and thromboxane A2 assists in aggregation, vasoconstriction and degranulation.
what is the initial step of secondary hameostasis?
platelets release calcium on surface (+ve surface) attracts -ve blood clotting factors
Damage tissue releases TF
what is are the steps in coagulation
TF activates VIIa
TF/VIIa then activate V/Xa – which activates prothrombin (factor 2) into thrombin (2a)
2a then activates fibrinogen and also VIII/IXa (and XI/XII)
VIII/Ixa reactivates V/Xa increasing fibrinogen (amplification)
what are the different classifications of causes of primary haemostasis?
Vascular (vessel wall)
Platelets
Von Willebrand Factor
What are the causes of vascular related primary haemostasis failure?
hereditary acquired ageing (lose collagen) scurvy steroid therapy Vasculitis – Henoch-Schonlein Purpura syndrome marfaarns syndrome
What are the causes of platelets related primary haemostasis failure?
thrombocytopenia
• reduced production – pancytopenia
• increased destruction, DIC, Autoimmune - Immune thrombocytopenic purpura (ITP), Hypersplenism
Reduced Function - drugs, renal failure
what is the cause of Von Willebrand disease?
autosomal dominant
what are the clinical features of primary haemostasis failure?
- Spontaneous Bruising and Purpura
- Mucosal Bleeding - Epistaxes, GI (mouth), Conjunctival, Menorrhagia
- Intracranial haemorrhage
- Retinal haemorrhages
how is primary haemostasis failure diagnosed?
platelet counts
what are the different causes of secondary haemostasis failure?
single clotting factor deficiency
multiple clotting factor deficiency
increased fibrinolysis
what are the causes of single clotting factor deficiency?
Haemophilia
what are the causes of multiple clotting factor deficiency?
Usually acquired
Liver failure
Vitamin K Deficiency - poor dietary intake, malabsorption, obstructive jaundice, warfarin therapy, haemorrhagic disease of new-born
Complex coagulopathy
DIC - microthrombus (end organ failure), clotting factor consumption (bruising, purpura, bleeding)
what are the clinical features of Failure of Secondary Haemostasis?
• No characteristic clinical syndrome • May be combined primary/secondary haemostatic failure • Pattern of bleeding depends on o Single/multiple abnormalities o The clotting factors involved
what are the two tests for failure of secondary haemostasis?
- prothrombin time (TF/VIIa) = measures initiation
* Activated partial Thromboplastin Time (VIII/IXa) = amplification
what is thrombophilia?
: Familial or acquired disorders of the haemostatic mechanism which are likely to predispose to thrombosis
what are the different mechanisms of thrombophilia?
Increased coagulation activity - Platelet plug or Fibrin clot formation
Decreased fibrinolytic activity
Decreased anticoagulant activity - decreased serine protease inhibitors, Protein C and Protein S
what are the clinical features of thrombophilia?
- DVT and PE
- Recurrent miscarriage
- Complications of pregnancy
- Purpura Fulminans (clotting disorder of newborn (give Vit K)
- Skin necrosis
what are the hereditary causes of thrombophilia?
- Factor V Leiden
- Prothrombin 20210 mutation
- Antithrombin deficiency
- Protein C deficiency
- Protein S deficiency
what are the features to consider hereditary thrombophilia screening?
o Venous thrombosis <45 years old o Recurrent venous thrombosis o Unusual venous thrombosis o Family history of venous thrombosis o Family history of thrombophilia
what is the management of hereditary thrombophilia?
- Advice on avoiding risk
- Short term prophylaxis - to prevent thrombotic events during periods of known risk
- Short term anticoagulation -to treat thrombotic events
- Long term anticoagulation - recurrent thrombotic events
what is acquired thrombophilia?
Antiphospholipid Syndrome
what are the causes of Antiphospholipid Syndrome?
o Autoimmune Disorders o Lymphoproliferative Disorders o Viral Infections o Drugs o Primary
what is the pathophysiology of APS?
- Antibodies cause conformational change in β2 glycoprotein 1 - activates primary and secondary haemostasis and vessel wall abnormalities.
- Autoantibodies have specificity for anionic phospholipids, can prolong phospholipid dependant coagulation tests in vitro
- Also known as Lupus anticoagulants
what are the clinical features of APS?
Recurrent thromboses - Arterial, including TIAs, Venous
• Recurrent fetal loss
• Mild thrombocytopenia (using up thrombin making clots)
how can APS be diagnosed?
- Prothrombin Time
* APTT
what is the management of APS?
- Activation of both primary and secondary haemostasis
- management of Arterial and venous thrombosis
- Aspirin
- Warfarin
what is the platelet level in TTP?
↓↓↓
what is the platelet level in ITP?
↓↓↓
what is the platelet level in HIT?
↓↓
what is the haemoglobin level in TTP?
↓↓
what is the haemoglobin level in ITP?
Normal
what is the haemoglobin level in HIT?
Normal
what is the LDH level in TTP?
↑↑↑
what is the LDH level in ITP?
Normal
what is the LDH level in HIT?
Normal
what is the indirect bilirubin level in TTP?
↑
what is the indirect bilirubin level in ITP?
Normal
what is the indirect bilirubin level in HIT?
Normal
what is the haptoglobin level in TTP?
↓
what is the haptoglobin level in ITP?
Normal
what is the haptoglobin level in HIT?
Normal
what is the reticulocyte level in TTP?
↑
what is the reticulocyte level in ITP?
Normal
what is the reticulocyte level in HIT?
Normal
what is the schistocyte level in TTP?
↑↑↑
what is the schistocyte level in ITP?
Normal
what is the schistocyte level in HIT?
↑
what is the underlying mechanism of Heparin-Induced Thrombocytopenia (HIT)?
Exposure to heparin/LMWH causes IgG autoantibodies to be formed against it
what i the pathophysiology of HIT?
- Exposure to heparin/LMWH → IgG autoantibodies formed against heparin → platelet factor 4 (PF4) binds to heparin →antibody-heparin-PF4 complex →increased platelet activation → thrombosis formation in arteries, veins
- Increased consumption of platelets for clotting + removal of antibody-heparin-PF4 complexes by macrophages of reticuloendothelial system →thrombocytopenia
what is the severity of Type 1 HIT?
Transient, mild, not clinically significant
what is the severity of Type 2 HIT?
Complications can be life-threatening
what is the onset of Type 1 HIT?
1-4 days after exposure