Lecture 4 - Introduction to Haemostasis and Thrombosis PDF

Introduction to haemostasis and thrombosis Kenneth S Charles MB.BS, FRCP, FRCPath (Haem).CCST Objectives Describe components of haemostatic system Understand basic laboratory principles Identify common bleeding and thrombotic disorders Understand principles of treatm...

Introduction to haemostasis and thrombosis Kenneth S Charles MB.BS, FRCP, FRCPath (Haem).CCST Objectives Describe components of haemostatic system Understand basic laboratory principles Identify common bleeding and thrombotic disorders Understand principles of treatment Why are we learning this? Thrombosis = clotting Haemorrhage = bleeding We are all in a constant state of balanced clot formation and clot breakdown Any disruption may lead to abnormal haemorrhage or thrombosis Both extremely common in clinical practice Introduction Clinical case Components of haemostatic system Principles of testing Platelets and clotting factors Bleeding and clotting disorders Clinical case 74 year old woman 15 days after Astra Zeneca COVID vaccine Pain, swelling left lower limb Doppler ultrasound shows femoral deep vein thrombus Platelet count 54 x 109/l D-Dimers 5.0 ng/ml (normal < 0.4) Clinical case 74 year old woman 15 days after Astra Zeneca COVID vaccine Pain, swelling left lower limb Doppler ultrasound shows femoral deep vein thrombus Platelet count 54 x 109/l D-Dimers 5.0 ng/ml (normal < 0.4) Platelets Produced by megakaryocytes in bone marrow Normal 150-400 x 109/l, < 10 x 109/l causes spontaneous bleeding Circulating half-life 10 days Central to primary hemostasis (initial closure of defect in vessel wall through formation of platelet plug) Procoagulant and anticoagulant factors in granules Activate clotting factors that bind to membrane surface Haemostatic System Platelets Vascular endothelium Procoagulant (clotting) proteins Natural anticoagulant proteins Fibrinolytic system Platelet functions Adhesion Release Aggregation Activation of clotting factors Platelet adhesion Platelet function Vessel injury Exposure of subendothelium Platelet binding Shape change (become spherical and extend pseudopods) Intracellular granules moved towards surface Release of contents Platelet function Platelet function Platelet function Activation of platelets results in exposure of GpIIb/IIIa and binding to fibrinogen exposure of the procoagulant phosphatidylserine surface for binding of coagulation proteins Tests of platelet function Complete blood count Blood film Bleeding time Platelet function analyzer 100 (PFA-100) Platelet aggregation tests Bleeding time PFA-100 Platelet aggregation tests Platelet disorders Deficiency Immune Thrombocytopenia - reduced platelet production Functional disorders Inherited: Bernard-Soulier (GpIb/IX) (GpIIb/IIIa) Storage Pool Disease Acquired: Aspirin, Renal failure Drug-induced autoimmune thrombocytopenia 61 yo female, platelet count 1 x 109/l Immune Thrombocytopenic Purpura 21 yo female, plt 3 x 109/l Immune Thromboctyopenia Immune thrombocytopenia Aspirin effect Non-steroidal anti-inflammatory agent therapy (Diclofenac) Coagulation factors Factors I XIII Most made in liver Activated sequentially to form clot (fibrin) Two pathways intrinsic/extrinsic Same end result fibrin clot Coagulation Cascade  Coagulation tests Add activator thromboplastin for extrinsic pathway, calcium and phospholipid for intrinsic pathway Measure time to clot Prothrombin Time (PT) for extrinsic pathway, Activated Partial Thromboplastin Time (APTT) for intrinsic pathway Coagulation cascade Thrombin is both coagulant and anticoagulant Procoagulant: activates I,V, VIII, XI, XIII Activates platelets Anticoagulant: activates protein C by binding to thrombomodulin Citrate tubes for coagulation tests Automated coagulometer Common coagulation problems Inherited: Factor VIII deficiency (Haemophilia A) Factor IX deficiency (Haemophilia B) Von Willebrand Factor Deficiency (VWD) Acquired: Anticoagulant therapy Disseminated intravascular coagulation (DIC) Factor VIII Cofactor in intrinsic pathway Synthesised by reticuloendothelial cells in liver Procoagulant activity Gene is on X chromosome Haemophilia A severe < 1%, moderate 1-5%, mild 5-30% normal activity Acute haemarthrosis Intracranial haemorrhage Severe Haemophilia A Haemophilic arthropathy  Coagulation tests Deficiencies cause prolongation of times depending on pathway to which deficient protein belongs Common coagulation problems Inherited: Factor VIII deficiency (Haemophilia A) Factor IX deficiency (Haemophilia B) Von Willebrand Factor Deficiency (VWD) Acquired: Anticoagulant therapy Disseminated intravascular coagulation (DIC) Factor VIII Cofactor in intrinsic pathway Synthesized by reticuloendothelial cells in liver Procoagulant activity Gene is on X chromosome Thrombosis Venous or arterial Excessive activity of coagulation proteins Vessel wall injury/inflammation Deficiency of natural anticoagulants Slowing of blood flow Risk factors for Venous Thromboembolism (VTE) Acquired Bed rest Plaster cast Trauma Major surgery Orthopaedic surgery Malignancy Oral Contraceptive Pill/ Hormone Replacement Therapy Age Obesity Laboratory tests in Haemophilia Solitary prolongation of APTT Factor Assay (VIII, IX) Risk factors for Venous Thromboembolism (VTE) Inherited Antithrombin deficiency Protein C deficiency Protein S deficiency Factor V Leiden (FVL) Prothrombin 20210A Natural anticoagulants Protein Function Antithrombin Inhibits IIa, IXa, Xa, XIa Protein C Inhibits Va, VIIIa Protein S Cofactor for protein C Tissue Factor Pathway Inhibits TF/VIIa Inhibitor (TFPI) Procoagulant (gain of function) mutations Factor V Leiden (increased Factor Va activity) Prothrombin 20210A (increased factor IIa activity) Deep Vein Thrombosis (DVT) Deep Vein Thrombosis (DVT) Enoxaparin and warfarin Drug Factors inhibited Heparin IIa, Xa Warfarin II, VII, IX, X Novel oral anticoagulants Xa Warfarin- induced intracranial haemorrhage Disseminated Intravascular Coagulation Sepsis/severe infection Malignancy (24%) Obstetric calamities (23%) Surgery, polytrauma, neurotrauma (19%) Liver disease (8%) Severe toxic or immunological reactions snake bites, transfusion reactions Laboratory features of DIC Microangiopathic haemolytic anaemia Thrombocytopaenia Prolonged PT, APTT Reduced fibrinogen Elevated FDPs, D-Dimers Von Willebrand Factor Synthesised in endothelial cells, megakaryocytes Small and large multimers Binds/protects factor VIII Platelet adhesion and aggregation Laboratory Diagnosis VWD APTT Bleeding time, Platelet Function Tests VIIIc VWFAg Ristocetin cofactor activity Multimer analysis DIC blood film DIC secondary to E. Coli septicaemia Processes in DIC Underlying disorder associated with DIC Systemic activation of anticoagulation Widespread fibrin deposition Consumption of platelets and clotting factors Microvascular Thrombocytopenia and coagulation thrombosis deficiency BLEEDING ORGAN FAILURE BJH, 145, 24-33 Heparin Induced Thrombocytopenia with Thrombosis Clinical diagnosis 5 days heparin 30% fall in platelet count Thrombosis Heparin Induced Thrombocytopenia with Thrombosis Vaccine Induced Prothrombotic Immune Thrombocytopenia 5 28 days after COVID vaccine (especially Astra Zeneca but all) Clots in abnormal sites sagittal sinus, splanchnic or more typical DVT/PE Virus induces anti-PF4 antibodies which activate platelets and endothelium Platelet consumption thrombocytopenia Rare about 1 in 100,000 Thrombosis risk Percentage Summary Describe components of haemostatic system Understand basic laboratory principles Identify common bleeding and thrombotic disorders Thank you