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Clinical Pathology > Lab Evaluation of Hemostasis II > Flashcards

Lab Evaluation of Hemostasis II Flashcards

1
Q

What is the classical coagulation pathways?

A

intrinsic
extrinsic

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2
Q

What is tissue factor?

A

glycoprotein receptor for FVII on the surface of subendothelial tissues

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3
Q

What are problems with the classical pathway?

A

deficiencies in prekallikrein (PK), high molecular weight kinonogen (HMK), and factor XII have prolonged coagulation test results for the intrinsic pathway

but animals with these deficiencies DO NOT have bleeding problems

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4
Q

T/F: If an animal is deficient in FXII, they will not bleed

A

TRUE

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5
Q

What is activated by thrombin in vivo?

A

FXI

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6
Q

What is the extrinsic pathway also called?

A

tissue factor pathway

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7
Q

What is the common pathway of coagulation?

A
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8
Q

What are some anticoagulants?

A

Ca2+ chelators - EDTA, citrate

heparin

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9
Q

T/F: The intrinsic pathway initiates coagulation

A

FALSE - extrinsic

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10
Q

What is heparin?

A

cofactor for antithrombin

inhibits thrombin (factor IIa) and factors IX and Xa

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11
Q

What do EDTA and citrate bind to in the classic coagulation pathway?

A

Ca2+ in the common pathway

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12
Q

Explain how heparin acts as an anticoagulant

A

is a proteoglycan

helps change structure so now it binds antithrombin tightly so that it can bind to thrombin and inhibit coagulation

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13
Q

____ + _____ inhibits thrombin

A

heparin
antithrombin

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14
Q

What are some coagulation/fibrinolysis screening tests?

A
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15
Q

If there is a problem with Activated Clotting Time (ACT), it will be a problem with which pathways?

A

intrinsic, common

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16
Q

If there is a problem with Activated Partial Thromboplastin Time (APTT), it will be a problem with which pathways?

A

intrinsic and/or common

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17
Q

If there is a problem with Prothrombin Time (PT), it will be a problem with which pathways?

A

extrinsic and/or common

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18
Q

If there is a problem with Thrombin Clotting Time (TCT), it will be a problem with which pathways?

A

extrinsic and/or common

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19
Q

What is activated clotting time (ACT)?

A

performed next to the animal
uses whole blood

special tubes are used
time for clot to form is recorded

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20
Q

How is APTT and PT tested?

A

blood is collected into citrate
blood centrifuged and plasma removed

plasma samples are kept cool and quickly submitted to a laboratory for testing

coagulation tests are initiated by adding calcium and appropriate activators

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21
Q

What are APTT false prolonged times?

A

delayed testing and/or warming of sample

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22
Q

What is thrombin clotting time a measure of?

A

measure of fibrinogen concentration

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23
Q

What is fibrinolysis?

A

lysis of clots

plasminogen by tPA —> plasmin —> fibrin —> FDPs

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24
Q

What is FDP latex bead agglutination?

A

anti-FDP IgG

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25
Q

What leads to increased FDP values?

A

DIC with secondary fibrinolysis because DIC has all of these clots so the body responds by producing plasmin to break fibrinogen down to fibrin to get rid of the clots

fibrinogenolysis - rattlesnake

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26
Q

What is the D-dimer test?

A

specific FDP molecule - best in dogs

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

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27
Q

What are d-dimers?

A

specific fibrin degradation product

28
Q

What leads to a low and high plasma concentration regarding vWf?

A

inflammation

dogs with liver disease, endotoxemia, following epinephrine, and during parturition

29
Q

What leads to a low plasma concentration?

A

von Willebrand disease

30
Q

What leads to low antithrombin?

A

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

31
Q

What leads to high antithrombin?

A

may increase as an acute phase protein in cats

32
Q

What are some coagulation defects?

A

spontaneous hematomas
hemarthrosis

33
Q

What are some acquired coagulation deficiencies?

A

DIC (factors V, VIII, and sometimes fibrinogen)

vitamin K deficiency (factors 2, 7, 9, 10) secondary to decrease absorption of vitamin K or rodenticide toxicity

Liver failure

certain snake venoms

34
Q

What is brodifacoum toxicity?

A

rodenticides

35
Q

How do rodenticide and warfarin affect vitamin K metabolism?

A

blocks enzyme needed to convert vitamin k epoxide (inactive) back to vitamin k hydroquinone (active)

36
Q

A vitamin K deficiency results in low ______

A

carboxylation

37
Q

How do snake venoms affect coagulation?

A

varies by snake

37
Q

What does the eastern diamondback rattlesnake venom do?

A

contains crotalase that lyses fibrinogen - blood does not clot

38
Q

With a snake bite, what would you expect the hemostatic tests to be?

A

platelets: normal
PT: >90 seconds
APTT: >70 seconds
FDP: positive (because fibrinolysis is occurring)

anticoagulation = prolonged bleeding times

39
Q

What factor is the animal first to bleed?

A

factor 2 - NOT XII

40
Q

What are some hereditary deficiencies of the intrinsic pathway?

A

factor XII
prekallikrein
high molecular weight kinogen
factor VI
factor IX
factor VIII:C

41
Q

Which factors in the intrinsic pathway do not bleed?

A

factor XII
prekallikrein
high molecular weight kininogen

42
Q

Which factors in the intrinsic pathway DO bleed?

A

big ones are 9 and 8c

43
Q

What is a hereditary deficiency of extrinsic pathway?

A

factor VII deficiency (bruising in beagle dogs)

44
Q

What are hereditary deficiencies of the common pathway?

A

factor X (cocker spaniels)
prothrombin (mild bleeding in dogs)
fibrinogen (dogs and goats)
deficiencies in factor V - not reported

45
Q

How do you get hereditary coagulopathy involving multiple coagulation factors?

A

vitamin k-dependent factors

46
Q

What is a hypercoagulable state? What is it also referred to as?

A

increased tendency for coagulation without clinical signs or laboratory evidence of thrombosis or DIC

thrombophilia or prethrombic state

47
Q

What are potential causes of hypercoagulable state?

A

initiatial reactions that ultimately lead to DIC or thrombosis

antithrombin deficiency: losing thrombin a small molecule

inherited and acquired protein C deficiency

48
Q

What is antithrombin?

A

the major inhibitor of thrombin and other coagulation factors

endothelial cells have heparin sulfate proteoglycans on their surfaces - and inhibit coagulation factors

binding of antithrombin to proteoglycans accelerates the inactivation serine protease coagulation factors

49
Q

With a damaged glomerulus, what happens to antithrombin?

A

seeps out

50
Q

What happens in DIC?

A

diffuse thrombosis and secondary fibrinolysis in small vessels

51
Q

What are some diseases that might initiate DIC?

A

septicemias and viremias
protozoal infections and metazoan parasites
marked tissue injury
intravascular hemolysis

52
Q

What does DIC form?

A

microthrombi in the body

53
Q

What is the pathway of DIC?

A
54
Q

What are the hemostatic trends for DIC?

A
55
Q

What does a thrombocytopenia with normal APTT, PT, and FDP tests mean?

A

lack of platelet production
increased destruction of platelets

56
Q

What does a thrombocytopenia with prolonged APTT and PT test results and a positive FDP test mean?

A

Consumption of both platelets and coagulation factors as occurs in DIC

Plasma antithrombin III concentration is generally low when measured.

All five abnormalities listed will not be present in every animal with DIC.

Of these assays, the PT test is most likely to be normal

57
Q

What does a normal platelet count, prolonged APTT & PT test results, & a negative FDP test mean?

A

Multiple coagulation defects, as can occur in rodenticide toxicity and liver disease

Inherited defect in the common coagulation pathway

Collection of blood from a heparinized IV line

Platelet counts may be decreased in animals subsequent to marked blood loss associated with rodenticide toxicity.

58
Q

What does a normal platelet count, APTT, and PT with a negative FDP test in the presence of a fibrinogen degradation bleeding diathesis (increased bleeding susceptibility) mean?

A

Platelet function defect or vascular injury

A concomitant prolonged bleeding time suggests a platelet function abnormality is present.

Inherited platelet abnormalities or vWD could be present.

59
Q

What is the pathogenesis of thrombosis?

A

endothelial cell activation or injury

altered blood flow

changes in coagulation factors, fibrinolytic factors, or their inhibitors

platelet activation

60
Q

With localized thrombosis, what would you expect the platelet counts, coagulation tests, and FDP values to be?

A

normal maybe

61
Q

What is arterial thrombosis often associated with?

A

localized damage to the endothelium

62
Q

What is venous thrombosis often associated with?

A

decreased blood flow

63
Q

What are causes of possible thrombosis?

A
64
Q

What is aortic thromboembolism in cats?

A

Clinical Pathology (11 decks)

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