BLEEDING DISORDERS Flashcards
what can cause reduced collagen
old age
steroid use
why can vitamin C deficiency cause failure of primary Haemostasis
its needed to make collagen
what are the four main mechanisms of bleeding disorder
failure of primary Haemostasis (platelet plug)
failure of secondary Haemostasis (fibrin clot)
excess fibrinolysis
excess anticoagulant defences
what are the three main reasons for failure of platelet plug formation
vascular
platelets
von willebrand factor
reasons for thrombocytopaenia
coagulopathy
autoimmune disorders
hypersplenism
marrow pathology
which drugs can cause problems with platelet function
NSAIDs
aspirin
warfarin
why can renal failure cause failure of primary Haemostasis
uraemia interferes with platelet function
what is the commonest cause of primary haemostatic failure
thrombocytopenia
describe the extrinsic pathway
TF > VIIa > V > Xa > thrombin > fibrin
describe the intrinsic pathway
thrombin > VIII/IXa > V > Xa > thrombin > fibrin
causes of multiple clotting factor deficiencies
liver failure (clotting factors are made in the liver) vitamin K deficiency complex coagulopathy
what can cause vitamin K deficiency
poor dietary intake malabsorption obstructive jaundice (bile salts needed to absorb vitamin K) vitamin K antagonists haemorrhage disease of the newborn
what is the function of vitamin K in the clotting cascade
it is needed to carboxylate factors II, VII, IX and X
as well as diet, how else is vitamin K obtained by the body
it is produced by gut bacteria
causes of DIC
sepsis
obstetric emergencies
malignancy
trauma
management of DIC
treat the underlying cause
supportive therapy
which coagulation pathway does prothrombin time reflect
extrinsic
which factors are measured by prothrombin time
fibrinogen prothrombin V VII X
which pathway does APTT reflect
intrinsic
which factors does APTT measure
fibrinogen prothrombin V VIII IX X XI XII
prolongation of both PT and APTT suggests….
general deficiency of both pathways
prolongation of PT suggests….
deficiency in the extrinsic pathway
prolongation of the APTT suggests…
deficiency in the intrinsic pathway
which substance breaks down fibrin
plasmin
give an example of a fibrin breakdown product the can be measured
D-dimer
why is D-dimer high in DIC but low in liver disease
it is high in DIC because there are high rate of fibrinolysis (lots of fibrin is being broken down)
it is low in liver disease because the liver is unable to produce the clotting factors in the first place
why is haemophilia rare in girls
it is X-linked
which part of the body is most commonly affected by haemophilia
joints eg ankle, knee, elbow
how does haemophilia cause joint damage
general activity causes bleeding in the joints (haemoarthosis)
iron in blood irritates the synovial leading to inflammation
inflammation causes neovascularisation with fragile blood vessels
fragile blood vessels are more likely to bleed, starting the cycle again
why does bleeding tend to occur from medium to large blood vessels in haemophilia
they still have platelets so small, minor bleeds can be healed, but large vessels would need a fibrin clot
clinical features of haemophilia
recurrent haemoarthroses
recurrent soft tissue bleeds
prolonged bleeding after dental extraction and invasive procedures
what is the difference between haemophilia A and B
A = factor VIII deficiency B = factor IX deficiency
