Clotting Flashcards
What is the difference between primary and secondary hemostatis
Primary hemostasis involves the initial, rapid response to vascular injury, forming a temporary platelet plug, while secondary hemostasis reinforces this plug with a fibrin mesh through the activation of the coagulation cascade
What is Prothrombin Time (PT)?
A primary tool for evaluating secondary hemostasis, specifically the extrinsic and common coagulation pathways.
PT is crucial for assessing the blood’s ability to clot, particularly in cases of bleeding disorders.
Which coagulation pathways does PT evaluate?
Extrinsic and common coagulation pathways.
These pathways are vital for normal blood clotting processes.
Why is the extrinsic pathway sensitive to vitamin K factors?
Due to factor VII’s short half-life.
Vitamin K is essential for the synthesis of several coagulation factors.
What factors are associated with the extrinsic pathway?
Factors III (tissue factor), VII, X.
Calcium play a role
What can cause an elevation in PT?
- fVII deficiency
- Early or low-dose itamin K antagonist
- Mild Vitamin K deficiency
- Early to mild hepatic insufficiency
These conditions can impair the coagulation process, leading to prolonged PT.
What does aPTT stand for?
Activated partial thromboplastin time
What aspect of hemostasis does aPTT evaluate?
Secondary hemostasis
Which pathways is aPTT associated with?
Intrinsic or common pathway
Name causes leading to elevated aPTT.
- Factor VIII, IX, or XI deficiency
- Unfractionated heparin
- DIC
- Severe vWF dz
- Hepatic failure
- Circulating anticoagulant
True or False: aPTT is only associated with the extrinsic pathway.
False
Fill in the blank: Elevated aPTT can be caused by ____ factor deficiencies.
fVIII, IX, or XI deficiency
What is one condition that can cause elevated aPTT related to blood coagulation factors?
Severe von Willebrand disease (vWF dz)
Which anticoagulant is associated with elevated aPTT?
Unfractionated heparin
What percentage drop in amount of a factor needed to see prolongation in PT and PTT?
25-30%
How should marked prolongation in PT and PTT be interpreted?
Usually significant
How should mild prolongation in PT and PTT be interpreted?
With caution
Is there value in assessing hypercoagulability with PT and PTT?
No value
What PT or aPTT level poses a risk for bleeding in surgery?
> 1.5x control
What are potential causes for prolonged PT or aPTT?
- fX deficiency
- V deficiency
- II deficiency
- Fibrinogen deficiency
- Vitamin K deficiency
- Hepatic failure
- DIC
- Massive bleeding
- Dilutional coagulopathy
- Unfractionated heparin
What pathway does Activated Clotting Time primarily measure?
Intrinsic and common pathway
Which factor is activated by Activated Clotting Time?
Factor XII
Is Activated Clotting Time more or less sensitive than aPTT?
Less sensitive than aPTT
What is the normal Activated Clotting Time for dogs?
Usually less than 110 sec
What is the normal Activated Clotting Time for cats?
Usually less than 75 sec
What substances can be used to activate factor XII in the context of Activated Clotting Time?
Whole blood + colite, kaolin, glass beads
What is another substance that induces Activated Clotting Time?
Diatomaceous earth
What is the primary use of D-dimers in medical testing?
Sensitive test for thromboembolism and DIC
Unknown if indicator of hypercoagulability or predictor of thrombosis
Which test is considered the best for diagnosing hypercoagulability?
TEG
TEG stands for Thromboelastography
In TEG, what does a hypercoagulable tracing indicate?
↑ G value; R and K values generally ↓ and/or MA and α values ↑
Indicates increased clot strength and reduced clotting time
What does an increase in MA in TEG testing suggest?
PLT hyperaggregability
Indicates increased platelet aggregation contributing to clot formation
What does a decrease in R value in TEG testing indicate?
Enzymatic hyperactivity
Suggests faster clot formation due to enhanced enzymatic activity
Fill in the blank: D-dimers are a sensitive test for _______.
thromboembolism and DIC
True or False: TEG is not useful for diagnosing hypercoagulability.
False
TEG is specifically used for this purpose
What is the role of platelets in primary hemostasis?
Provide a source of preformed chemokines stored in intracellular storage granules
What do activated platelets synthesize that helps in recruiting and activating additional platelets?
Secondary agonists: prostanoids (TxA2) and ADP
Which pathway is TxA2 produced by via the platelets?
COX-1 pathway
Thromboxane A2 (TxA2), a prostanoid produced by platelets through the COX-1 pathway, is a potent vasoconstrictor and platelet activator, playing a crucial role in thrombosis and cardiovascular health
What happens once the platelet integrin alphaIIbBeta3 is activated by an agonist?
Binding domains for fibrinogen are exposed, leading to interplatelet cohesion and aggregation
Platelet integrin αIIbβ3 (also known as GPIIb/IIIa) is activated by agonists through a process called “inside-out signaling,” where agonists induce conformational changes that increase the integrin’s affinity for its ligands.
True or False: Platelets play more of a role in secondary hemostasis than primary hemostasis.
False
Platelets play a larger role in primary hemostasis
