Secondary Hemostasis Flashcards
Requirements of ACT coagulation test
Whole Blood
Contact Activator
Significance of prolonged Thrombin Time
Quantitative or qualitative abnormalities of fibrinogen
Inhibitors of fibrin formation
_______________ is required for the initation of secondary hemostasis when initiated by wounds
Tissue Factor
Result of Disseminated Intravascular Coagulation (DIC)
Thrombosis of the microvasculature
Depletion of coagulation factors and platelets → bleeding
Significance of prolonged PT
Factor VII deficiency
Deficiency or inhibition of common pathway factor
Inhibitor Consumption Tests
Antithrombin (AT)
Requirements for PT coagulation test
Citrated plasma
Tissue factor
Calcium
Platelet substitute
Cause of Disseminated Intravascular Coagulation (DIC)
Continued activation of coagulation and fibrinolysis
Induction or exposure of tissue factor or other activators of coagulation
Endothelial damage exposing collagen
Proteolytic enzymes
Stagnant blood flow
Increased concentration of D-Dimers occurs wtih
Increased fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearance of FDP by liver
Coagulation test for the common pathway
Fibrinogen
TT
Tissue Factor Pathway Inhibitor inhibits
Generation of Xa
Loads of thrombin generated on the platelet surface drives the formation of
Fibrin
Thromibin time measures
Time for fibrin clot formation in citrated plasma + thrombin
Inhibitors of coagulation
Antithrombin
Activated Protein C (APC)
Tissue Factor Pathway Inhibitor (TFPI)
Alpha-2 Macroglobulin
Significance of fibrinogen concentration increase
Inflammation
Relative increase with dehydration
Two phases of DIC
Hypercoagulabile Phase
Consumptive Phase
Steps of the Common Pathway of the Coagulation Cascade
- X → Xa
- Prothrombin → Thrombin by Xa
- Fibrinogen → Fibrin by Thrombin
Vitamin K dependent Factors?
II, VII, IX, X
Categories of coagulation tests
Procoagulant Tests
Anticoagulat Tests
PIVKA would be increased in
Vitamin k antagonism/deficiency
Human hepatocellular carcinomas
Hypercoagulable Phase of DIC
Thrombosis
Ischemic necrosis and organ dysfunction
Prothrombin Time (PT) measures
Time for fibrin clot formation in citrated plasma + tissue factor + calcium + platelet phospholipid substitute
Clinical signs of DIC
Associated with the signs of primary disease
Signs of organ dysfunction secondary to thrombosis
Bleeding
Requirements of aPTT coagulation test
Citrated Plasma
Contact activator
Calcium
Platelet substitute
Plasmin degrades fibrin into
Fibrin Degradation Products
D- Dimers
Pathogenesis of the hypercoagulable phase of DIC leading to organ dysfuction
Thrombus formation → blockage of the microvasculature → Ischemic necosis → Organ dysfunction
Hemophilia B
Factor IX deficiency
Dogs and Cats
Signs and inheritance patterns similar to Hemophilia A
Requirements for Thrombin Time coagulation test
Citrated plasma
Thrombin
Mechanism of action of Antithrombin
- Heparin binds to antithrombin
- Heparin causes conformational change and exposes the thrombin binding site
- Thrombin binds to AT = TAT complex and heparin floats away
- Tat Comples is cleared by the phagocytic system
Secondary Hemostasis
Stabilization of the platelet plug via fibrin meshwork - used in large defects
Laboratory findings in Warfarin Toxicity
PT - prolonged
aPTT, ACT - prolonged
PIVKA - positive
Platelet count - normal
Three phases of the cell-based model
Initiation
Amplification
Propagation
Why does vitamin k antagonism work?
Vitamin K dependent factors los their negative charge and are not recruited to sites of injury
Hageman’s Disease
Factor XII deficiency
Cats and Killer Whales
Deficiency not associated with bleeding - prolonged PTT
Secondary hemostasis occurs on
Platelet surface
Fibrin Degradation Products inhibit
Platelet function and fibrin polymerization
Which of the intrinsic pathway coagulation tests is more sensitive?
aPTT
Laboratory findings of hemophilia A
Platelet Count - Normal
Bleeding Time - Normal
aPTT and ACT - Prolonged
PT- normal
Factor activity - reduced
Pathophysiology of Warfarin Toxicity
Coumarins block enzymes required to reduce vitamin K
Negative charge not transferred to coagulation factors
Platelet surface charge remains positive
Factors X and II unable to bind to platelet
Coagulation factors are synthesized in the
Liver
Treatment of warfarin toxicosis
Decontamination
Supplement vitamin K
Plasma and/or blood transfusions
Fibrinolytic Activity Tests
Fibrin Degradation Products
D-Dimer
How is citrated plasma different than blood?
No RBC, WBC or Platelets
Decreased Calcium
Key factor that promotes amplification of secondary hemostasis
Thrombin
For collection of blood for coagulation tests, what tube should be used?
Blue Top - Citrate Tube
Factors involved in the Intrinisc Pathway
XII, XI, IX, VIII
X is converted to Xa by what in the Intrinisc Pathway?
IXa
Activated Protein C inhibits
Va, VIIa
Coagulation test for the intrinsic pathway
aPTT
ACT
aPTT and ACT tests measure
Time for fibrin clot formation
Factors involved in the Extrinsic Pathway
Tissue Factor III
VII
Pathways that make up the coagulation cascade
Intrinsic pathway - Contact Activation
Extrinsic pathway - Tissue Activation
Common Pathway
Clinical features of Warfarin Toxicosis
Bleeding - Anemia, weakness, pallor, hypovolemia, shock, dyspnea, lameness, neurologic signs
Death
What is the cardinal bloodwork finding for a patient in consuptive phase of DIC?
Thrombocytopenia
Significance in fibrinogen concentration decrease
Consumption due to hypercoagulation - excessive conversion of fibrinogen to fibrin
Decreased production by the liver
Pathogenesis of hypercoagulable phase of DIC leading to bleeding
Thrombus formation → fibrinolysis → increased FDPs → decreased platelet function → bleeding
Significance of prolonged aPTT and ACT time
Deficiency or inhibition of any intrinsic or common pathway factor
Heparin therapy
IX is converted to IXa in the Intrinsic Pathway by
VIIa
Coagulopathy and Liver disease
Decreased synthesis of coagulation factors
Production of dysfunctional factors
X is converted to Xa by what in the Extrinisic Pathway
VIIa
Treatment for DIC
Identify and eliminate underlying disorder
Fluid therapy
Transfusion therapy
Hemophilia A
Factor VIII deficiency
X linked recessive inheritance
Causes mild, moderate or severe bleeding
Non-Enzymatic factors of the coagulation cascade
Tissue Factor (Factor III, Thromboplastin)
Factor VIIIa
Factor Va
Calcium
Platelets
Factors affected by amplification
XI
VII
VIIIa
Va
Coagulation Tests
Activated Partial Thromboplastin Time (aPTT, PTT)
Prothrombin Time (PT)
Thrombin Time (TT), Fibrinogen
PIVKA
Special Factor Assay
PIVKA
Proteins induced by vitamin K antagonism
Indirectly measures abnormal forms of vitamin K dependent factors
Increased concentration of fibrin degradation products occus when
Increased fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearance of FDP by liver
Antithrombin inhibits
Thrombin, IXa, Xa
VII is converted to VIIa in the extrinsic pathway by
Xa
Fibrinogen is an indicator of what in large animals
Inflammation
Laboratory findings of DIC
Thrombocytopenia
PT, aPTT - Prolonged
Fibrinogen - decreased
FDP and D-Dimers - increased
Antithrombin - decreased
Hemorrhagic anemia
Schistocytes
aPTT requires ______% deficiency before prolongation is detected
70%
ACT requires ______% deficiency of factor before prolongation is detected
95%
Serum biochemistries for DIC depend on
Primary Disease
Location of microthrombosis
PT requires ______% deficiency of factor before prolongation is detected
70%
Alpha-2 Macroglobulin inhibits
Thrombin
Plasmin
Kallikrein
Prothrombin is converted to Thrombin by
Xa
Enzymatic Factors of the Coagulation Cascade
XII, XI, IX, VII, X
Prothrombin
Thrombin
Fibrinogen
Fibrin
Pathogenesis of consumptive phase of DIC
Depletion of coagulation factors and platelets → bleeding
Fibrinogen is converted to Fibrin by
Thrombin
Activated Clotting Time ACT measures
Time for fibrin clot formation in non-anticoagulated whole blood
Coagulation test for the extrinsic pathway
PT
Plasminogen is converted to Plasmin by
Tissue Plasminogen Activator (TPA)
Inherited Factor Deficiencies
Hemophilia A - VIII
Hemophilia B - IX
Hagemans Disease - XII
Factors involved in the common pathway
X, V
Prothrombin
Fibrinogen
Fibrin
Cell Based Model
Focuses on the roll of cells involved with coagulation
Why is PT a good choice in test for screening for Vitamin K deficiency?
Because Factor VII has the shortest half life
Causes of Warfarin Toxicosis
Poisoning with coumarin derivatives
Fat malabsorption
Dietary deficiency
Antibiotics that cause decreased absorption or utilization by liver
It is good practice to supplement a patient with prolonged aPTT with what before surgery?
Plasma