Coagulation

Question 1

What are the aspects of primary haemostasis?

Answer 1

Vasoconstriction

Platelet adhesion and aggregation

Question 2

What are the aspects of secondary haemostasis?

Answer 2

Activation of coagulation factors

Formation of fibrin meshwork

Question 3

Describe the process of coagulation

Answer 3

Initiation phase: injury of vessel wall leads to contact between blood and endothelial cells, tissue factor (TF) is exposed and initiates coagulation (activates other factors)
Amplification phase: other factors convert prothrombin to thrombin, which results in further platelet and factor activation
Propagation phase: platelet and factor activation by thrombin feeds back to increase thrombin production, “thrombin burst” results in conversion of fibrinogen to fibrin to form a stable clot

Question 4

How is thrombin inactivated?

Answer 4

Binds to thrombomodulin, antithrombin, heparin, etc.

Question 5

What is ACT?

Answer 5

Activated clotting time

Question 6

What is APTT?

Answer 6

Activated partial thromboplastin time

Question 7

What is PT and INR?

Answer 7

Prothrombin time

International normalised ratio (adjusts of differences in reagent used)

Question 8

What is the normal PT?

Answer 8

~18 secs

Question 9

What is the normal INR?

Answer 9

1

Question 10

What is the ideal INR for a patient on warfarin?

Answer 10

2-3

Question 11

How are PT and INR interpreted?

Answer 11

Higher = increased risk of bleeding or warfarin use
Lower = increased risk of clotting