pt aptt technical information
TRANSCRIPT
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PT & aPTT
Manish Pandey
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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
Formation of Blood Clot (thrombus) in normal blood vessels
Thrombotic occlusion of a vessel after relatively minor injury
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Hemostasis involves the interaction of:
Vascular EndotheliumPlateletsCoagulation 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
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Secondary HemostasisFibrin is required to stabilize the primary platelet plugFibrin is formed by two coagulation pathways i.e. Extrinsic & IntrinsicExtrinsic 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
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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 XII
PT prolonged, aPTT normalDeficiency of extrinsic Pathway factor VIIOccasionally, mild to moderate deficiency
of common pathway factor(s) fibrinogen, II, V or x
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Both PT and aPTT ProlongedDeficiency 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
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)
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Mixing studies in aPTT
Treat specimen with heparinase (degrades heparin)
aPTT normal, prolongation due to heparin aPTT prolonged
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 dimer
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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
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Fibrinolysis
or Kallikrein from Intrinsic PathwayPlasminogen 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 XIIa
2.Protein C and Protein S – Vitamin K dependent proteins, inactivate Factors Va and VIIIa
3.Plasmin
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Fibrin Degradation Products or FDP’s include:
fragments X and Y – early splits and D and E – late splitsD-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, & X
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Liver DysfunctionFibrinogen and Factor XIII deficiencyFactor XI and Contact Activation Antithrombin Deficiency leads to DVT and
PEvon Willebrand Disease: Deficiency of von
Willebrand Factor
Clinical Significance of Hemostasis
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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 results
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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: AspirinStreptokinase, urokinase injectionst-PA injections
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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
INR =
ISI
