Haemostasis Flashcards
Describe the laboratory tests used to assess the clotting system?
FBC: To detect a thrombocytopenia
INR/Prothrombin Time: Measures activity of the extrinsic pathway. Raised with warfarin.
APTT (activated partial thromboplastin time): Measures activity of the intrinsic pathway. Raised with heparins
TT (thrombin time): test the common pathway it is prolonged by any heparin but particularly UFH.
Note: the INR is derived from the prothrombin time.
What are the scenarios that would cause a raised INR/prolonged prothrombin time?
Vitamin K deficiency as it is needed for clotting factors 2,7,9 and 10. (1972).
Liver disease as the liver produces factors 2 and 7 (aswell as several other factors)
DIC (all your clotting factors get used up)
Warfarin as it blocks the activation of Vitamin K.
What are the scenarios in which you would see a prolonged APTT?
- Haemophillia A and B
- Von Willerbrands disease
- Liver disease as it produces factors I, IV, V and VI.
- DIC
- Lupus anticoagulant* in a test tube causes prolonged clotting in vivo it causes clots.
Describe the importance of the liver in clotting?
The liver produces factors: I (fibrinogen), II (prothrombin), IV, V, VI, and VII. Decreases in any of these will result in increased prothrombin times (INR).
Portal hypertension leads to splenomegaly, and increased sequestration of platelets there.
Vitamin K is fat soluble, and therefore requires bile salts for absorption – cholestasis will reduce vit K supply.
Describe the importance of Vitamin K in clotting?
Vitamin K is involved in the carboxylation of glutamate residues in the production of clotting factors:
II, VII, IX and X. 1972
Warfarin is a Vitamin K antagonist.
How should you investigate any patient presenting with easy bruising?
Take a good bleeding history including: any previous procedures did they need blood. How heavy periods are etc.
FBC and blood film.
INR and APTT.
If these are abnormal you can use mixing studies* to identify whether there is a factor deficiency or a factor inhibitor.
*Mix patient blood with normal serum, if factor deficiency then this should correct, if there is an inhibitor then there should still be prolonged bleeding.
What is haemophilia?
It is an X linked hereditary bleeding disorder.
2 types
A: Factor VIII deficiency
B: Factor IX deficiency
How is haemophilia usually present?
40% present in the neonatal period with:
- intracranial haemorrhage
- oozing from the heel prick
- post circumcision
Can present with recurrent spontaneous bleeding into joints and muscles which can lead to arthritis
Often presents with bruising around 1 year of age when infants start to walk.
How is haemophilia categorised?
By degree of deficiency
Mild: 5-40% Bleeding after after surgery
Moderate: 1-5% Bleeding after minor trauma
Severe: Less than 1% spontaneous bleeding into joints
How is haemophilia managed?
Treatment is recombinant factor 8 or 9 depending on type A or B.
Given prophylactically and when actively bleeding.
Lifestyle measures aka avoid contact sport.
What is von Willebrand’s disease?
A deficiency in von Willebrand factor (responsible for platelet adhesion and as a carrier protein for factor VIII).
They therefore have problems with factor VIII deficiency and platelet adhesion.
It is caused by a variety of mutations, inheritance is usually dominant.
How does von Willebrand’s disease usually present?
The most common form is usually mild and often not diagnosed till puberty or adulthood.
Presents with:
- Bruising
- Prolonged bleeding post surgery
- Mucosal bleeding
Spontaneous bleeding is uncommon.
How is von Willebrand’s disease treated?
Treated with synthetic vasopressin as it causes secretion of factor VIII and vWP.
Used in caution in under 1’s as can cause hyponatraemia and seizures.
NSAIDs, aspirin and IM injections should be avoided.
How does Warfarin work and how is it monitored?
Warfarin blocks the regeneration of Vitamin K from its epoxide
Vitamin K is a cofactor for gamma cogaulation of the following coagulation factors: II, VII, IX and X
It is monitored using the INR with the target range usually being between 2-3 (in unmedicated people normal is 1-2)
How is over coagulation with warfarin managed?
If you can wait 12 hours use iv/po Vitamin K (10mg for complete reversal, 0.5-1mg for reduction in INR)
If immediate reversal is needed use FFP (Fresh Frozen Plasma) 1L is needed therefore there is a risk of overloading.
In fluid restricted patients that require immediate reversal Prothrombin Complex Concetrate* should be given via a haematology consultant.
*Concentrated factors II, VII, IX and X
