Coagulation Flashcards
What is involved in primary haemostasis?
vasoconstriction, platelet adhesion, platelet aggregation
How long does primary haemostasis take?
second to minutes
What is involved in secondary haemostasis?
activation of coagulation factors and formation of fibrin
How long does secondary haemostasis take?
minutes
What is involved in fibrinolysis?
lysis of the clot
When does fibrinolysis occur?
minutes to hours
What are the three abnormalities that influence thrombosis (virchow’s triad)?
abnormalities of the vessel wall, abnormalities of blood flow, abnormalities of blood composition
Is it possible to clinically test the integrity of the vessel wall?
No
Is the coagulation system redundant?
Yes - if one part of the system is functioning another part may be able to compensate
What is the key enzyme in coagulation?
thrombin
What is the initiating protein in coagulation?
tissue facctor
Do the extrinsic and intrinsic pathways explain the physiological process?
No
What are the three phases of coagulation?
Initiation phase, amplification phase, propagation phase
What occurs in initation phase?
Tissue factor is exposed and starts off the whole cascade
What occurs in the amplification phase?
thrombin starts to be generated - this gives positive feedback and amplifies the amount of thrombin generated
What happens in the propagation phase?
thrombin burst leads to the formation of fibrin - the clot that plugs the hole
What is the action of thrombin?
converts fibrinogen to fibrin, cross links fibrin, positive feedback, bind thrombomodulin, activates TAFI, activates platelets
How is thrombin inactivated?
Binding to thrombomodulin
What types of haemostatic tests can be done?
Can measure the number, function and appearance of platelets or can measure coagulation system
What are the different types of coagulation system tests?
global, specific or genotyping
What are the key principles of coagulation tests?
sample integrity is crucial, need a standard curve to compare to controls, duplicate testing needs to be done and an abnormal test doesn’t mean abnormality - test needs to be repeated and to match history
What are the global tests for bleeding?
ACT, APTT, PT/INR, thrombin generation
What are the specific tests for bleeding?
factor assays, von willebrand factor, collagen binding assays, fibrinogen
What is a functional clot based assay?
A test which measure clotting time but is difficult technically
What is a chromagenic assay?
A test which measures light to represent protein functions - doesn’t reflect physiology but is easily reproducible
What is an immunological assay?
A test which measures the amount of protein - this test does not tell you anything about function - can have patients with a normal amount and low function
What is a PT test?
Test which measures clotting time via the extrinsic system
What is a PT ratio?
To normalise results in a PT test
What is an INR test?
An international normalised ratio - a PT ratio raised to the power of the international sensitivity index - gives the same result world wide - a normal result is around 1
What is an APTT test?
A test which measures clotting time via the intrinsic system - results are specific for the lab that you are in
Which test would you use if the patient is on warfirin?
INR
Which test would you use if the patient was on heparin or lupus anticoagulant?
APTT
What factors does Warfirin inhibit?
Vitamin K dependent factors - II, VII, IX, X
