Clotting cascade

Question 1

Give another term for clotting factor III

Answer 1

Tissue factor

Question 2

What is factor II called? What is factor IIa called? Which factor is responsible for activating factor II?

Answer 2

Prothrombin
Thrombin
Factor Xa

Question 3

What is factor I called? What is factor Ia called? What is responsible for activating factor I?

Answer 3

Fibrinogen
Fibrin
IIa (aka thrombin)

Question 4

Which factors are part of the extrinsic pathway? What is it activated by? What is its goal? Which laboratory test corresponds to this pathway?

Answer 4

III, VII
External damage
Activation of factor X to factor Xa
Prothrombin time (PT)

Question 5

Which factors are part of the intrinsic pathway? What is it activated by? What is its goal? Which laboratory test corresponds to this pathway?

Answer 5

VIII, IX, XI, XII
Spontaneous internal damage to the vascular endothelium
Activation of factor X to factor Xa
Activated Partial Thromboplastin Time (APTT)

Question 6

Which factors are part of the common pathway? What is it activated by? What is its goal? Which laboratory test corresponds to this pathway?

Answer 6

X, V, II, I
VIIa (extrinsic) or IXa with VIII as a cofactor (intrinsic)
Formation of fibrin clot
Both PT and APTT

Question 7

Which factors are vitamin K dependent? Where is vitamin K produced? What kind of symptoms will appear if vitamin K is not being produced?

Vitamin K deficiency can also be due to poor absorption - Is vitamin K water or fat soluble? What are the other vitamins in the same category? Where are they absorbed? What kind of pathology can inhibit absorption?

Answer 7

II, VII, IX, X
Liver
Liver failure can present with increased bleeding and slow clotting

Fat soluble
A, D, E, K
Terminal ileum
Crohn’s, Coeliacs, Chronic pancreatitis, Ileal resection (among others)

Question 8

What is the mechanism of action of Warfarin? Why might a patient be placed on warfarin? (Bonus - what risk score might be relevant here?) What lab test is used to monitor patients on warfarin? What is the target range if the patient is on warfarin vs not on warfarin?

Answer 8

Vitamin K antagonist
To prevent stroke in AF (bonus CHA2D2VASc = risk of stroke in AF), prosthetic heart valve, venous thromboembolism
INR (International normalised ratio) - PT expressed as a ratio
On warfarin: Target 2-3
Not on warfarin: Target around 1

Question 9

Name 2 types of anticoagulant medication, their mechanisms of action and which pathways of the clotting cascade they act on.

Why might you prescribe one over the other?

Answer 9

Warfarin - Vitamin K antagonist. All 3 pathways: II and X (common), VII (extrinsic), IX (intrinsic)

DOAC (eg. apixaban, rivaroxaban) - Factor Xa inhibitor. Common pathway

Warfarin needs regular monitoring to ensure anticoagulation, DOACs don’t
Warfarin has a longer half-life than DOACs - Warfarin may be better if patient is prone to forgetting to take medication