This document summarizes normal hemostasis and abnormalities that can lead to thrombosis or bleeding disorders. It describes the intrinsic and extrinsic coagulation pathways, factors involved, and tests used to evaluate them. Abnormalities in these pathways can cause bleeding disorders like hemophilia or thrombosis. Disseminated intravascular coagulation is also discussed, where initial thrombosis leads to widespread activation of coagulation and bleeding. Treatment options like oral anticoagulants, heparin, and fibrinolytics are mentioned.

1. PT & aPTT PROF.DR. MOHAMMAD SOROUR CONSULTANT HAEMATOLOGY B.C.H.

2. Hemostasis Is a Balance Between Clot Formation & Clot Dissolution.

3. Normal Hemostasis Clot formation (Coagulation) Clot dissolution (Fibrinolysis) PT aPTT Thrombin Time Fibrinogen Individual factor tests FDP D-Dimer vWF HMWK Prekallikrein

4. Thrombosis Abnormal Hemostasis is Thrombosis Formation of Blood Clot ( thrombus) in normal blood vessels Thrombotic occlusion of a vessel after relatively minor injury

5. Hemostasis involves the interaction of: Vascular Endothelium Platelets Coagulation Factors and Fibrinolytic Proteins

6. Hemostasis has 2 main functions: Induce a rapid & localized hemostatic plug at the site of vascular injury (clot formation) Maintain Blood in a fluid, clot-free state after the injury is healed (clot dissolution)

8. Primary Hemostasis Injury Endothelial Cells Exposure of thrombogenic surface (subendothelial extracellular matrix)

9. Platelets adhere and get activated Change shape Release secretory granules (e.g. ADP, TXA2) Attract other platelets and Aggregate Hemostatic plug or Primary Platelet Plug

10. Secondary Hemostasis Fibrin is required to stabilize the primary platelet plug Fibrin is formed by two coagulation pathways i.e. Extrinsic & Intrinsic Extrinsic Pathway is initiated when Tissue Factor (III) present in damaged organ comes in contact with Blood Intrinsic Pathway is initiated when Factor XII binds to a negatively charged “foreign” surface exposed to Blood

11. Coagulation Factors Factor Trivial Name Pathway Prekallikrein Fletcher factor Intrinsic HMWK Contact activation cofactor Intrinsic I Fibrinogen Both II Prothrombin Both III Tissue Factor Extrinsic IV Calcium Both

12. V Proaccelerin, Labile factor Both VI (Va) Accelerin Both VII Proconvertin Extrinsic VIII Antihemophilic factor A Intrinsic XI Antihemophilic factor B Intrinsic

13. XII Hageman Factor Intrinsic XIII Fibrin Stabilizing factor Both

17. PT and aPTT testing PT ( Prothrombin Time) test is done for deficiency of factors of extrinsic pathway aPTT ( activated Partial Thromboplastin Time) test is done for deficiency of factors of Intrinsic pathway

18. Effects of Hereditary or Acquired Factor Deficiency on the PT & aPTT aPTT prolonged, PT normal Deficiencies of intrinsic pathway Factor(s) VIII, IX, XI or XII PT prolonged, aPTT normal Deficiency of extrinsic Pathway factor VII Occasionally, mild to moderate deficiency of common pathway factor(s) fibrinogen, II, V or x

19. Both PT and aPTT Prolonged Deficiency of common pathway factor(s) fibrinogen, II, V, or X Multiple factor deficiencies

20. Mixing studies in PT PT mixing study (1:1 mix of patient and normal plasma PT normalizes Factor Deficiency; Measure factors I, II, V, VII, X PT initially shortens and then prolongs Factor V inhibitor (rare) aPTT remains prolonged Inhibitor (specific factor inhibitor, rare) Treat specimen with heparinase (degrades heparin) PT normal, prolongation due to heparin PT prolonged

21. Mixing studies in aPTT aPTT mixing study (1:1 mix of patient and normal plasma aPTT normalizes Factor Deficiency; Measure factors VIII, IX, XI, XII aPTT initially shortens and then prolongs Factor VIII inhibitor aPTT remains prolonged Inhibitor, most commonly Lupus Anticoagulant Treat specimen with heparinase (degrades heparin) aPTT normal, prolongation due to heparin aPTT prolonged

23. Fibrinolytic Mechanism Stable Fibrin Clot Activation of Protein C and Protein S Secretion of t-PA by endothelial cells Plasminogen Plasmin Stabilized fibrin clot X, Y fragments Plasmin Degrades D-E-D fragments E fragment + D dimer

24. Fibrinolysis As soon as the injury is healed clot dissolution starts, to restore the normal flow of Blood Plasminogen is converted to the active form Plasmin by 2 distinct Plasminogen Activators (PAs): tissue plasminogen activator (t-PA) from injured endothelial cells Urokinase from Kidney endothelial cells and plasma

25. Fibrinolysis or Kallikrein from Intrinsic Pathway Plasminogen can also be activated by the bacterial product (e.g. Streptokinase) – having significance in certain Bacterial Infections Free Plasmin is neutralized by α 2- plasmin inhibitor (PAI) t-PA activity is also blocked by PAI

26. Endothelial cells modulate the coagulation / anticoagulation balance by releasing PAIs PAIs block fibrinolysis by inhibiting t-PA binding to fibrin as it is most active when bound to fibrin

27. Fibrinolysis Three types of Natural Anti-coagulants regulate clotting: antithrombin III – inhibit thrombin activity and Factors IXa, Xa, XIa and XIIa Protein C and Protein S – Vitamin K dependent proteins, inactivate Factors Va and VIIIa Plasmin

28. Fibrin Degradation Products or FDP’s include: fragments X and Y – early splits and D and E – late splits D-Dimer is the smallest cross-linked FDP

29. D-Dimer are specific FDP formed only by Plasmin activity on fibrin clot and not on intact fibrinogen Thus the presence of D-Dimer indicates that fibrin has been formed and so is a marker for an ongoing in vivo thrombotic condition

30. Clinical Significance of Hemostasis Hemophilia A: Caused by the deficiency of Factor VIII Hemophilia B: Caused by the deficiency of Factor IX Vitamin K deficiency (PIVKA’s) P rotein I nduced V itamin K A ntagonism can be used in thrombotic conditions Vitamin K dependent factors are II, V, IX, & X

31. Clinical Significance of Hemostasis Liver Dysfunction Fibrinogen and Factor XIII deficiency Factor XI and Contact Activation Antithrombin Deficiency leads to DVT and PE von Willebrand Disease: Deficiency of von Willebrand Factor

32. DIC (Disseminated Intravascular Coagulation) Massive Injury or Sepsis Massive release of Tissue Factor III Excessive Activation of Thrombin Coagulation becomes systemic

33. High consumption of Platelets, coagulation factors Over production of fibrin clot Fibrin clot “disseminates” or spreads throughout the microcirculation Obstructing the blood flow to capillaries, smaller vessels

34. Lack of blood supply leads to tissue injury (decreased oxygenation, organ infarction & necrosis) Once again release of Tissue Factor Second time coagulation activation More consumption of coagulation factors and platelets

35. Continuous thrombi formation Production capacity of Bone Marrow and Liver reaches its maximum level Activation of fibrinolysis at first site High consumption of Plasmin, antithrombin, Protein C and Protein S

36. Generation of Thrombin & Plasmin at the same time Plasmin acts on Fibrin Clots and produces FDPs and D-Dimer FDPs interfere with platelet function and impair fibrin clot formation Further bleeding results

37. Thus an initial thrombotic disorder gets converted into a serious bleeding disorder Whenever there is a widespread activation of Thrombin the chances are that it may lead to DIC

38. Pharmacological Intervention Most commonly patients are on OAC (oral anti-coagulant) therapy: warfarin – over dose can lead to Vit. K deficiency heparin Fibrinolysis: Aspirin Streptokinase, urokinase injections t-PA injections

39. INR & ISI values All PT reagents are calibrated against WHO IRP (International Reference Preparation) International Normalisation Ratio is intended to make comparison similar irrespective of the type of PT reagent used worldwide International Sensitivity Index is a measure of the sensitivity of particular PT reagent

40. Insensitive PT reagents will give prolonged results only when factor levels are very low Sensitive PT reagent give prolonged results even when there is a mild change in factor level Insensitive PT reagents have higher ISI values Sensitive PT reagents have ISI value as close to 1.0 as possible

41. Calculation of PT results INR = (Ratio) ISI Patient PT Time (secs) Mean Normal PT (MNPT) MNPT = Mean PT Time of at least 20 known normal samples INR = ISI

42. Thanks Please send your feedbacks to: Priyank Dubey Ph: 09999990845 [email_address] Application Specialist