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1. Normal haemostasis
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Haemostasis is the process whereby haemorrhage following vascular injury is arrested. It depends on closely linked interaction between: the vessel wall; platelets; coagulation factors. The fibrinolytic system and inhibitors of coagulation ensure coagulation is limited to the site of injury.
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Haemorragic diatheses Vasopathies (vessel wall dysfunction) Thrombocytopenias/-pathias Coagulopathies (inherited, aquired) Mixed type (vWD, DIC)
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Coagulation factors are proenzymes (serine proteases) and procofactors which are activated sequentially. The cascade has been divided on the basis of laboratory tests into intrinsic, extrinsic and common pathways
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Laboratory tests of coagulation.
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Screening test (normal range) Abnormalities indicated (prolonged abnormal) Most common cause of disorder Prothrombin time (PT) (10– 14s) Extrinsic and common coagulation pathways Deficiency/inhibition of factor VII, factors X, V, II and fibrinogen Liver disease, Warfarin therapy, DIC Activated partial thromblastin time (APTT or PTTK) (30–40s) Intrinsic and common coagulation pathways Deficiency/inhibition of one or more of factors XII, IX, VIII, X, V, II and fibrinogen Heparin therapy, haemophilia A and B, DIC Thrombin time (14–16s)Deficiency or abnormality of fibrinogen; inhibition of thrombin by heparin or FDPs DIC, heparin therapy, fibrinolytic therapy Fibrin degradation products (<10mg/mL) Accelerated destruction of fibrinogen DIC Platelet aggregation testsAbnormal platelet functionDrugs (e.g. aspirin), uraemia, von Willebrand’s disease
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Disorders of coagulation I: inherited
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Factor VIII deficiency (haemophilia A)
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Clinical features Range from severe spontaneous bleeding, especially into joints (haemarthroses) and muscles, to mild symptoms. Onset in early childhood. Increased risk of postoperative or post-traumatic haemorrhage. Chronic debilitating joint disease caused by repeated bleeds.
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Severity Mild (>5% activity of the f.VIII) Moderate (2-5%) Severe (<2%) All the lab tests normalize at the activity level of >10%. Patients with mild form don’t have spontaneous bleeding.
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Laboratory features Prolonged activated partial thromboplastin time (APTT), normal prothrombin time (PT), normal bleeding time, Plasma factor VIII reduced Carriers have factor VIII approximately 50% of normal. DNA analysis is helpful in carrier detection and counselling. Von Willebrand factor level is normal.
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Treatment Plasma exchange, cryoprecipitate, native plasma concentrate, Infusions of factor VIII concentrate to elevate the patient’s level to 20–50% of normal for severe bleeding. Level is raised to and maintained at 80–100% for elective surgery. Desmopressin, an analogue of vasopressin, leads to a modest rise in endogenous factor VIII which is useful in mild cases. Avoid aspirin, other antiplatelet drugs and intramuscular injections. Patients should be registered with a recognized haemophilia centre and should carry a card with details of their condition.
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Complications of treatment HIV and hepatitis C from impure preparations, subsequent AIDS, hepatitis and cirrhosis. Neutralizing antibodies to factor VIII in 15% of severe patients may require immunosuppressive therapy, treatment with porcine factor VIII (during a week - max), Feiba, Novoseven
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Von Willebrand’s disease
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Is usually autosomal dominant, results from mutations in the von Willebrand factor (vWF) gene. Von Willebrand factor is a large multimeric protein produced by endothelial cells, which carries factor VIII in plasma and mediates platelet adhesion to endothelium. The disease is more frequent than haemophilia A; males and females are affected equally.
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Clinical features Bleeding, typically from mucous membranes (mouth, epistaxes, menorrhagia). Excess blood loss following trauma or surgery. Haemarthroses and muscle bleeding are rare.
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Diagnosis APTT is prolonged, PT normal. Factor VIII and vWF levels are reduced. Bleeding time is prolonged. Defective platelet function, reduced aggregation with ristocetin. Mild thrombocytopenia may occur.
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Treatment Intermediate purity factor VIII concentrate (contains both vWF and factor VIII) for bleeding. Desmopressin is helpful for mild bleeding. Fibrinolytic inhibitors (e.g. tranexamic acid) are helpful.
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Disorders of coagulation II: acquired
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Vitamin K deficiency (liver disease, mechanical jaundice) Disseminated intravascular coagulation Drugs (warfarin) Acquired coagulation inhibitors
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Thank you for your attention. Questions are welcome!
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