PT & aPTTPROF.DR. MOHAMMAD SOROUR

CONSULTANT HAEMATOLOGY

B.C.H.1

Hemostasis Is a Balance Between Clot Formation & Clot Dissolution.

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Normal Hemostasis

Clot formation(Coagulation)

Clot dissolution(Fibrinolysis)

PTaPTT

Thrombin TimeFibrinogen

Individual factor tests

FDP D-Dimer

vWFHMWK

Prekallikrein

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Thrombosis

Abnormal Hemostasis is Thrombosis

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Formation of Blood Clot (thrombus) in normal blood vessels

Thrombotic occlusion of a vessel after relatively minor injury

Hemostasis involves the interaction of:

• Vascular Endothelium• Platelets• Coagulation Factors and • Fibrinolytic Proteins

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Hemostasis has 2 main functions:1. Induce a rapid & localized hemostatic plug at

the site of vascular injury (clot formation)

2. Maintain Blood in a fluid, clot-free state after the injury is healed (clot dissolution)

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Primary Hemostasis

Injury

Endothelial Cells

Exposure of thrombogenic surface (subendothelial extracellular matrix)

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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 9

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

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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 11

V Proaccelerin, Labile factor

Both

VI (Va) Accelerin Both

VII Proconvertin Extrinsic

VIII Antihemophilic factor A Intrinsic

XI Antihemophilic factor B Intrinsic

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XII Hageman Factor Intrinsic

XIII Fibrin Stabilizing factor Both

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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

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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 XIIPT prolonged, aPTT normal• Deficiency of extrinsic Pathway factor VII• Occasionally, mild to moderate deficiency of

common pathway factor(s) fibrinogen, II, V or x

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Both PT and aPTT Prolonged• Deficiency of common pathway factor(s)

fibrinogen, II, V, or X • Multiple factor deficiencies

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Mixing studies in PT

Treat specimen with heparinase (degrades heparin)

PT normal, prolongation due to heparin PT prolonged

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PT mixing study (1:1 mix of patient and normal plasma

PT normalizes

Factor Deficiency;Measure factorsI, II, V, VII, X

PT initially shortens and then prolongs

Factor V inhibitor (rare)

aPTT remains prolonged

Inhibitor (specific factor inhibitor, rare)

Mixing studies in aPTT

Treat specimen with heparinase (degrades heparin)

aPTT normal, prolongation due to heparin aPTT prolonged

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aPTT mixing study (1:1 mix of patient and normal plasma

aPTT normalizes

Factor Deficiency;Measure factorsVIII, IX, XI, XII

aPTT initially shortens and then prolongs

Factor VIII inhibitor

aPTT remains prolonged

Inhibitor, most commonly Lupus Anticoagulant

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Fibrinolytic MechanismStable 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 dimer23

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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

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 α2- plasmin inhibitor (PAI)

• t-PA activity is also blocked by PAI

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• 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

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Fibrinolysis

Three types of Natural Anti-coagulants regulate clotting:1.antithrombin III – inhibit thrombin activity and Factors IXa, Xa, XIa and XIIa2.Protein C and Protein S – Vitamin K dependent proteins, inactivate Factors Va and VIIIa3.Plasmin

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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

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• 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

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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) Protein Induced Vitamin K Antagonism

can be used in thrombotic conditions• Vitamin K dependent factors are

II, V, IX, & X30

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

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DIC (Disseminated Intravascular Coagulation)

Massive Injury or Sepsis

Massive release of Tissue Factor III

Excessive Activation of Thrombin

Coagulation becomes systemic

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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

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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

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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

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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 results36

• 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

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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 38

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

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• 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

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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

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INR =

ISI

Thanks

• Please send your feedbacks to:

• Priyank Dubey• Ph: 09999990845• priyank.exp@gmail.com• Application Specialist

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