L33: Lab investigation Bleeding Disorders

Question 1

what is the first priority when investigating a bleeding disorder in an animal? Then what?

Answer 1

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)

Question 2

What tests can you use to assess primary haemostasis

Answer 2

Platelet count –> e.g. thrombocytopenia
Blood smear –> platelet count and morphology
Buccal mucosal bleeding time

Question 3

To decide if an animal is genuinely thrombocytopaenic (automated haematology analysers often underestimate platelet count) what is it imperative that you always do!

Answer 3

Assess degree of thrombocytopaenia on blood smear (especially at feathered edge)

Question 4

How low does a platelet count drop before an animal is likely to develop haemorrhages

Answer 4

below 25 x 10^9/ L (ref 200-55 x10^9)

Question 5

What tests are accessible to assess secondary haemostasis?

Answer 5

Activated coagulation time (ACT) (in house)
Prothrombin time (PT)
Activated partial thromboplastin time (APTT)

Question 6

How do you run an ACT assay?

Answer 6

discard first blood (tissue factor), collect 2mL venous blood. Tube has intrinsic coagulation activator, should clot 64-95 sec (dog) <65 sec (cat)

Question 7

what are important factors to take into consideration when running an ACT assay?

Answer 7

Tube is body temp
discard first venous blood (tissue factor)
leave undisturbed 45 seconds then tilt every 5 seconds

Question 8

What specifically does ACT assess?

Answer 8

intrinsic & common pathways of coagulation cascade

Question 9

Under what circumstances will an ACT test be prolonged?

Answer 9

clotting factors in intrinsic or common pathway is less than 5-10% normal activity

*so normal result doesn’t exclude a clotting factor problem

Question 10

What type of blood is used to run a PT & APTT assay

Answer 10

venous blood
discard first mL (tissue factor)
placed in sodium citrate tube (FILL CORRECTLY)

Question 11

What does PT assess?

Answer 11

extrinsic & common pathways of coagulation cascade

Question 12

When might PT be prolonged?

Answer 12

if clotting factors in extrinsic or common pathway are less than 30% of normal activity

Question 13

What does APTT assess

Answer 13

intrinsic and common pathways of the coagulation cascade

Question 14

When might APTT be prolonged?

Answer 14

if clotting factors of intrinsic and common pathways are less than 30% normal activity

Question 15

What type of haemostasis do PT & APTT assess?

Answer 15

secondary haemosasis (time for fibrin clot to form)

Question 16

What diagnostic test would you run for a young male German shepherd dog w/ haemophilia A?

Answer 16

factor VIII is in intrinsic pathway, so use APTT (prolonged)

PT will be normal

Question 17

What coagulation test result would you expect in a beagle with inherited factor VII deficiency ?

Answer 17

factor VII extrinsic pathway, so PT will be prolonged

APTT and ACT normal

Question 18

What coagulation test would you use for an animal with suspected rodenticide poisoning?

Answer 18

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

Question 19

What coagulation test results would you expect in an animal bleeding due to liver cirrhosis

Answer 19

ACT, APTT, PT

Question 20

What haemostatic test results would you expect in an animal bleeding due to vWBD?

Answer 20

Normal platelet count
Prolonged buccal mucosal bleeding time
ACT, PT, APTT normal

Question 21

What haemostatic test results would you expect in an animal bleeding due to DIC?

Answer 21

At least 3 of…

Thrombocytopaenia 
Prolonged APTT/ PT
Shistocytosis on smear 
Hypofibrinogenanaemia 
INC blood conc fibrin degradation products