Lecture 33

Question 1

What type of blood sample do you need to run PT and APTT assays?

Answer 1

venous blood sample collected via clean venipuncture (with the first mL or so of blood discarded to prevent contamination with tissue factor) and placed immediately into a sodium citrate anticoagulant tube and then gently mixed

Question 2

What does the PT assess?

Answer 2

The PT assesses the extrinsic and common pathways of the coagulation cascade.
-NOT a particularly sensitive assay.

Question 3

What does the APTT assess?

Answer 3

The APTT assesses the intrinsic and common pathways of the coagulation cascade.
-NOT a particularly sensitive assay (but it is more sensitive than the ACT is).

Question 4

What coagulation test results would you expect in a young male German shepherd dog with hemophilia A (inherited deficiency of factor 8)?

Answer 4

Because factor VIII is in the intrinsic pathway, the APTT would be prolonged but the PT would be normal

Question 5

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

Answer 5

Because factor VII is in the extrinsic pathway, the PT would be prolonged (if the activity of factor VII was below 30% of normal) but the APTT and ACT would be normal.

Question 6

What coagulation test results would you expect in an animal that is bleeding due to
rodenticide anticoagulant consumption?

Answer 6

Because factor VII (in the extrinsic pathway) has the shortest half-life of the vitamin K-dependent factors (factors II, VII, IX and X), the PT will be the first coagulation test result to be prolonged in animals with vitamin K antagonism.
Eventually all.

Question 7

What coagulation test results would you expect in an animal that is bleeding due to
advanced chronic liver disease (e.g. cirrhosis) and hence inadequate synthesis of
coagulation factors?

Answer 7

Because hepatocytes are responsible for synthesis of most of the coagulation factors in circulation, you would expect the ACT, APTT and PT to all be prolonged

Question 8

What haemostatic test results would you expect in an animal that is bleeding due to von
Willebrand’s disease?

Answer 8

The platelet count would be expected to be normal.
The buccal mucosal bleeding time would be expected to be prolonged.
The ACT, PT and APTT would be expected to be normal.

Question 9

What haemostatic test results would you expect in an animal that is bleeding due to
disseminated intravascular coagulation (DIC)?

Answer 9

Animals in DIC that are presented for bleeding are expected to have thrombocytopenia (due to consumption of platelets) and impaired coagulation (due to consumption of clotting factors and enhanced fibrinolysis). Test results that should ring ALARM BELLS for DIC are a combination of thrombocytopenia and prolonged ACT, PT and APTT

Question 10

What other tests are readily available in Australia to confirm a suspicion of DIC?(5)

Answer 10

• thrombocytopenia
• prolongation of the APTT and/or PT
• erythrocyte fragmentation (schistocytes) on a peripheral blood smear
• hypofibrinogenaemia
• increased blood concentration of fibrin degradation products (FDP)