Notes on Hemostasis Disorders

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There is normal anticoagulation in small blood vessels:

• Heparin-like molecules: enhance Antithrombin III activity.

• Prostaglandin I2 activated.

• Protein C and S activated.

• Tissue Plasminogen Activator activated.

Procoagulants released in small vessel injury:

• Thromboxane A2: conversion of prostaglandin I2 to Thromboxane A2 by Thromboxane synthase.

• Von Willebrand Factor: platelet adhesion molecule.

• Factor VIII:C.

• Tissue thromboplastin (factor III).

Receptors for chemicals released by platelets:

• Von Willebrand Factor: GpIb.

Fibrinogen:

• GpIIb:IIIa; inhibited by ticlopidine and clopidogrel and abciximab.

Coagulation system:

• Extrinsic vs intrinsic.

Coagulation pathway: Extrinsic vs Intrinsic:

Coagulation pathway: extrinsic vs intrinsic

Vitamin K-dependent factors:

• Factors II, VII, IX, X; proteins C and S.

• Warfarin, an anticoagulant, inhibits vitamin K activity.

Fibrinolytic system:

• Activation by tPA; release of plasmin.

Thrombolytic therapy:

• Alteplace + reteplase (forms of tPA).

Activators of plasminogen:

• Factor XIIa, streptokinase, anistreplase, urokinase.

Small vessel hemostasis response to injury:

Vascular:

• Vasoconstriction after injury.

Platelet:

• Platelet adhesion; release reaction; platelet plug.

Coagulation:

• Thrombin production.

Fibrinolytic:

• Fibrin monomers cleaved by plasmin.

Tests:

• Ristocetin cofactor assay: vWF test.

• Platelet aggregation test: platelets.

• Prothrombin time: tests VII, X, V, II, I; inhibited by warfarin; 11-15 seconds.

• Partial thromboplastin time: tests XII, XI, IX, VIII, X, V, II, I; inhibited by heparin; 25-40 seconds.

• Fibrinogen degradation products: detect plasmin activity.

• d-Dimer assay: detects fibrin in fibrin clots.

Platelet disorders:

Thrombocytopenia:

• Decreased platelet count.

• Decreased production (anemia, leukemia) or increased destruction (idiopathic thrombocytopenic purpura, drugs; thrombotic thrombocytopenic purpura).

Yhrombocytosis:

• Increased platelet count.

• Eg., essential thrombocytopenia, polycythemia vera.

• Eg., iron deficiency, infections, splenectomy, malignancy.

Findings:

• Epistaxis, petechia, ecchymoses.

Coagulation disorders:

• Decreased production; eg., hemophilia A, cirrhosis.

• Inhibition; antibodies against coagulation factors.

• Consumption; DIC.

Findings:

• Late rebleeding; excessive bleeding.

Hemophilia A:

• XR disorder.

• Deficient VIII:C.

• Bleeding problems.

• Treatment: desmopressin acetate.

Hemophilia B:

• Christmas disease.

• Deficient factor IX.

Classic von Willebrand disease:

• AD disorder.

• Deficient vWF and VIII:C.

• Easy bleeding.

• Increased PTT; normal PT.

• Treatment: desmopressin acetate, oral contraceptives.

Vitamin K deficiency:

• Activates factors II, VII, IX, X, and proteins C and S.

Causes of deficiency:

• Breast milk lacks vitamin K.

• Prolonged antibiotic treatment.

• Decreased bowel absorption of vitamin K.

• Decreased vitamin K activation by liver epoxidase reductase.

Findings:

• GI bleeding, intracranial hemorrhage.

• Treatment: give vitamin K.

Disseminated intravascular coagulation:

Causes:

• Sepsis; disseminated malignancy like cancer, etc.; crush injuries, rattlesnake venom.

• Activated coagulation cascade.

• Fibrin thrombin in circulation.

• Fibrinolytic system activation.

• Increased PT/PTT; decreased fibrinogen.

• Thrombocytopenia, increased bleeding time.

• Fibrinolysis abnormalities.

• Treatment: treat underlying disease.

Primary fibrinolysis:

Causes:

• Open heart surgery.

• Liver disease.

• Prostatectomy.

• Fibrin degradation products interfere with platelet aggregation.

• Severe bleeding.

• Increased PT/PTT.

Secondary fibrinolysis:

• Compensatory reaction in presence of DIC.

Thrombosis syndromes: acquired thrombosis syndromes:

Antiphospholipid syndrome:

• SLE, HIV.

• Antiphospholipid antibodies present.

• Arterial and venous thrombosis syndromes; repeated abortions; strokes; thromboembolisms.

Causes:

• Folate / vitamin B12 deficiency, oral contraceptives, hyperviscosity.

Hereditary thrombosis syndromes:

• AD syndromes.

• Deep venous thrombosis.

Factor V-Leiden:

• Most common.

Antithrombin III deficiency:

• Prolongation of PT and PTT.

Protein C and S deficiency:

• Treatment: warfarin.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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