pt aptt 1218181287688715 8

PT & aPTTPROF.DR. MOHAMMAD SOROUR

CONSULTANT HAEMATOLOGY

B.C.H.1

Hemostasis Is a Balance Between Clot Formation & Clot Dissolution.

2

Normal Hemostasis

Clot formation(Coagulation)

Clot dissolution(Fibrinolysis)

PTaPTT

Thrombin TimeFibrinogen

Individual factor tests

FDP D-Dimer

vWFHMWK

Prekallikrein

3

Thrombosis

Abnormal Hemostasis is Thrombosis

4

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

5

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)

6

7

Primary Hemostasis

Injury

Endothelial Cells

Exposure of thrombogenic surface (subendothelial extracellular matrix)

8

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

10

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

12

XII Hageman Factor Intrinsic

XIII Fibrin Stabilizing factor Both

13

14

15

16

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

17

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

18

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

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

19

Mixing studies in PT

Treat specimen with heparinase (degrades heparin)

PT normal, prolongation due to heparin PT prolonged

20

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

21

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

22

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

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

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

25

• 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

26

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

27

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

28

• 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

29

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

31

DIC (Disseminated Intravascular Coagulation)

Massive Injury or Sepsis

Massive release of Tissue Factor III

Excessive Activation of Thrombin

Coagulation becomes systemic

32

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

33

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

34

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

35

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

37

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

39

• 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

40

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

41

INR =

ISI

Thanks

• Please send your feedbacks to:

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

42