L33: Lab investigation Bleeding Disorders Flashcards
what is the first priority when investigating a bleeding disorder in an animal? Then what?
control haemorrhage
combat shock if there are signs
then take detailed history + v thorough physical examination (single system vs. multiple etc., underlying cause, primary or secondary haemostats)
What tests can you use to assess primary haemostasis
Platelet count –> e.g. thrombocytopenia
Blood smear –> platelet count and morphology
Buccal mucosal bleeding time
To decide if an animal is genuinely thrombocytopaenic (automated haematology analysers often underestimate platelet count) what is it imperative that you always do!
Assess degree of thrombocytopaenia on blood smear (especially at feathered edge)
How low does a platelet count drop before an animal is likely to develop haemorrhages
below 25 x 10^9/ L (ref 200-55 x10^9)
What tests are accessible to assess secondary haemostasis?
Activated coagulation time (ACT) (in house)
Prothrombin time (PT)
Activated partial thromboplastin time (APTT)
How do you run an ACT assay?
discard first blood (tissue factor), collect 2mL venous blood. Tube has intrinsic coagulation activator, should clot 64-95 sec (dog) <65 sec (cat)
what are important factors to take into consideration when running an ACT assay?
Tube is body temp
discard first venous blood (tissue factor)
leave undisturbed 45 seconds then tilt every 5 seconds
What specifically does ACT assess?
intrinsic & common pathways of coagulation cascade
Under what circumstances will an ACT test be prolonged?
clotting factors in intrinsic or common pathway is less than 5-10% normal activity
*so normal result doesn’t exclude a clotting factor problem
What type of blood is used to run a PT & APTT assay
venous blood
discard first mL (tissue factor)
placed in sodium citrate tube (FILL CORRECTLY)
What does PT assess?
extrinsic & common pathways of coagulation cascade
When might PT be prolonged?
if clotting factors in extrinsic or common pathway are less than 30% of normal activity
What does APTT assess
intrinsic and common pathways of the coagulation cascade
When might APTT be prolonged?
if clotting factors of intrinsic and common pathways are less than 30% normal activity
What type of haemostasis do PT & APTT assess?
secondary haemosasis (time for fibrin clot to form)
What diagnostic test would you run for a young male German shepherd dog w/ haemophilia A?
factor VIII is in intrinsic pathway, so use APTT (prolonged)
PT will be normal
What coagulation test result would you expect in a beagle with inherited factor VII deficiency ?
factor VII extrinsic pathway, so PT will be prolonged
APTT and ACT normal
What coagulation test would you use for an animal with suspected rodenticide poisoning?
Factor VII of extrinsic pathway has shortest half-life of VitK dependent factors (2, 7, 9, 10) will be prolonged. So PT will be first coagulation test prolonged.
However, ACT, APTT, PT would all be prolonged eventually
Platelets normally within reference
What coagulation test results would you expect in an animal bleeding due to liver cirrhosis
ACT, APTT, PT
What haemostatic test results would you expect in an animal bleeding due to vWBD?
Normal platelet count
Prolonged buccal mucosal bleeding time
ACT, PT, APTT normal
What haemostatic test results would you expect in an animal bleeding due to DIC?
At least 3 of…
Thrombocytopaenia Prolonged APTT/ PT Shistocytosis on smear Hypofibrinogenanaemia INC blood conc fibrin degradation products
