18 - Laboratory Evaluation of Hemostasis 2

Question 1

what are the major components of hemostasis

Answer 1

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Question 2

what is the problem with the classical pathway for coagulation

Answer 2

• deficiencies in perkallikrein (PK), high molecular weight kininogen (HMK), and factor XII have prolonged coagulation test results for the intrinsic pathway
• however, animals with deficiencies in PK, HMK, and Factor XII do not have bleeding problems
• factor XI activated by thrombin in vivo

Question 3

what are anticoagulants

Answer 3

Ca+2 chelators: EDTA and citrate

Heparin
– cofactor for antithrombin
– inhibits thrombin (factor IIa) and factors IXa and Xa

Question 4

list the screen tests for coagulation/fibrinolysis

Answer 4

• activated clotting time (ACT)
• activated partial thromboplastin time (APTT)
• prothrombin time (PT)
• Thrombin clotting time (TCT)
• fibrinogen
• fibrin degradation products (FDPs) including D- dimer test

Question 5

what is activated clotting time (ACT) test

Answer 5

uses whole blood and it preformed next to the animal
- uses special tubes containing an activating substance
- tube maintained at 37C

• The time for clot to form is recorded

Question 6

what is ACT a measure of

Answer 6

intrinsic and common pathways

Question 7

what APTT and PT tests

Answer 7

blood is collected into citrate as the anticoagulant and the blood is centrifuged and plasma is removed
— plasma samples are kept cool and quickly submitted to a lab for testing

coagulation tests are initiated by adding calcium and activators and the time for clot to form is determined electronically

Question 8

what can cause APTT falsely prolonged times

Answer 8

• delayed testing or warming of sample
• low plasma to citrate ratio
  ——- insufficient blood collected into premeasured tube
  ——- erythrocytosis

Question 9

what can cause increased FDP values

Answer 9

• DIC with secondary fibrinolysis*
• also fibrinogenolysis (as occurs form crotalase in easter diamondback rattlesnake venom)
• exercise, anxiety, stress

Question 10

what is the D-dimer test

Answer 10

specific FDP molecule
- D-dimer is only present when cross-linked fibrin is lysed by plasmin

Question 11

when should the D-dimer test be negative

Answer 11

D-dimer test should be negative if only fibrinogenolysis is present

Question 12

viscoelastic coagulation assays

Answer 12

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Question 13

what does a low plasma concentration mean in plasma von willebrand factor

Answer 13

von willebrand disease

Question 14

what does a high plasma concentration mean in plasma von willebrand factor

Answer 14

• inflammation *
• dogs with liver disease, endotoxemia, following epinephrine, during parturition
• IL-11 stimulates synthesis
• desmopressin (DDAVP) stimulates transiently releases vWF from endothelial cell stores

Question 15

what could cause low plasma antithrombin

Answer 15

-hypercoagulable states
- DIC
- protein-losing nephropathies
- protein - losing enteropathies
- sometimes sepsis

Question 16

what can cause high plasma antithrombin

Answer 16

may increase an an acute phase protein in cats

Question 17

what are 2 physical signs of coagulation defects

Answer 17

• spontaneous hematomas
• hemarthrosis

Question 18

what are acquired coagulation deficiencies

Answer 18

• DIC (factor V, VIII, and sometimes fibrinogen)
• vitamin K deficiency (factors II, VII, IX and X) secondary to decrease absorption of vitamin K or rodenticide toxicity
• liver failure (multiple factors)
• certain snake venoms (variable)

Question 19

brodifacoum toxicity

Question 20

what are some hemostatic effects of snake venoms

Answer 20

** hemostatic effects vary depending on the type of snake*

• induce coagulation
• stimulate fibrinolysis and or fibrinogenolysis
• activate platelets
• activate or injury endothelium