10: Haemostasis Flashcards
How do platelets adhere to the vessel wall?
By vWF
What is the end point of platelet plug formation?
Fibrinogen to fibrin
What happens to blood vessels immediately following injury?
Reflex vasoconstriction
Where is vWF exposed from following injury?
The subendothelial matrix
Where are clotting factors produced?
Liver
Which factors require vitamin K?
II, VII, IX, X
What is the target for rodenticides?
Vitamin K
What is the end-point of the coagnulation cascade?
Produce thrombin to catalyse fibrin production
Which tests evaluate the intrinsic and common pathways?
APTT/ACT
Which test evaulates the extrinsic pathway?
OSPT
What activates the intrinsic pathway?
Negatively charged surface
What activates the extrinsic pathway?
Tissue factor
Which pathway is the most important initiator of secondary coagulation?
Extrinsic
What activates factor VII?
Exposure to tissue factor
What does factor VII activation cause?
Rapid thrombin burst
What is the function of the intrinsic pathway?
Amplification - causes cascade of activation via common pathway
Which factors does thrombin activate?
V, VIII, IX but also their inhibitors protein C and protein X
How does factor XIII stabilise the clot?
Forms covalent bonds that crosslink fibrin
Which breed gets hyperfibrinolytic disorders?
Greyhounds
What is activated by fibrinogen to cause fibrinolysis?
Plasmin
What does fibrinolysis result in production of?
FDPs e.g. D dimers
What are clinical signs or primary coagulation disorder?
Petechiae/ecchymoses, epistaxis, GI bleed
Below what platelet count do you see clinical signs in primary coagulation disorder?
30-50
Why are signs more severe in secondary coagulation disorder?
No stabilisation
What are some complications of secondary coagulation disorders?
Cavity bleed, haematomas
What should you test if primary coagulation disorder?
Platelets
What should you test if secondary coagulation disorder?
Clotting factors
What is a normal number of platelets per 100x field?
10-15
Below what platelet count per 100x field is there a risk of bleeding?
3-5
Which test should you not do in thrombocytopenia?
BMBT - check platelet count first
Why shouldn’t you do a cuticle bleed test in primary coagulation disorder?
If accidentally cut and arteriole it will involve secondary haemostasis so not a good test
Which are the most important tests for secondary haemostasis?
OSPT and APTT
How should you prepare the sample for secondary haemotasis test?
Non-clotted, citrate not EDTA
Which pathways does whole blood clotting times evaulate?
Intrinsic and common
Why is whole blood clotting time crude and insensitive?
Lots of other things influence, need adequate platelets to work
How does drawing blood into glass tube activate clotting?
Has -ve charge
How is activated clotting time more controlled than whole blood?
Temperature and diatomaceous earth for charge
What is the problem with activated clotting time test?
Still needs platelets, insensitive
Which pathways does APTT test?
Intrinsic and common
What’s an advantage of APTT test?
Doesn’t need platelets (but still not sensitive)
Above what % of reference control time is APTT abnormal?
20-25%
Which pathways does OSPT activate?
Extrinsic and common
WHat is the difference between OSPT and APTT?
OSPT provides TF as activator
What test do you do if you suspect fibrinogen deficiency/dysfunction?
Thrombin clotting time
How do you do the thrombin clotting time test?
Add thrombin to patients plasma to convert fibrinogen to fibrin
How do you detect FDPs?
Latex agglutination
What levels are FDPs normally?
Lowe
Under what conditions are FDPs high?
With fibrinolysis e.g. DIC, iliac thrombosis, internal haemorrhage
Why are FDP levels influenced by liver or kidney dysfunction?
This is how they are normally removed
In what condition are D-dimers high?
DIC
In what condition are D-dimers midrange?
Non-specific e.g. neoplasia, inflammation
What are D-dimers produced from?
Cross-linked fibrin
What does TEG test evaulate?
Clot formation and breakdown (clotting time and size)
What does TEG assess that other tests can’t?
Hypercoagulability and hyperfibrinolysis
