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clinical pathology > 17 - Laboratory Evaluation of Hemostasis 1 > Flashcards

17 - Laboratory Evaluation of Hemostasis 1 Flashcards

1
Q

what are the steps of hemostasis

A

1- vascular spasm

2- platelet plug formation

3- blood clotting

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2
Q

vascular injury?

A
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3
Q

what is the life span of platelets in mammals

A

4-6 days

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4
Q

what is platelet senescence

A

increased membrane phosphatidylserine (PS)

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5
Q

how are aged platelets removed

A

by macrophages

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6
Q

where are some platelets stored

A

splenic storage

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7
Q

what do platelets do

A
  • hemostasis
  • vascular integrity
  • various roles in inflammation and tumor metastasis
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8
Q

how do platelets cause hemostasis

A

platelet plug formation and they accelerate coagulation

** platelet procoagulant activity (prev. called platelet factor 3 PF3)
** platelet factor 4 - binds heparin and inhibits antithrombin activity

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9
Q

how do platelets adhere to the extracellular matrix

A

there is a GPlb/IX/V is a glycoprotein adhesion molecule complex on the platelet
—-> that binds to von Willebrand factor on the extracellular matrix

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10
Q

what shape change happens in platelets

A

unactivated platelets are round in shape and activated platelets develop filapodia

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11
Q

activation of platelet fibrinogen receptors

A

photo

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12
Q

activated platelets promote coagulation in vivo

A
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13
Q

what are 3 important hemostatic screening tests

A
  • platelet counts
  • mean platelet volume
  • buccal bleeding time
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14
Q

what can platelet clumps cause during a platelet count

A

a false thrombocytopenia

– caused by platelet activation during blood collection and handling (esp. cats)
– EDTA anticoag ( Esp. horses)

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15
Q

how can you rule out false thrombocytopenia

A

verify by stained blood film examination

– automated platelet counts often unreliable in cats

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16
Q

what dog breeds tend to have lower platelet counts

A
  • greyhounds
  • polish ogar dogs
  • cavalier king charles spaniels
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17
Q

what does an increased MPV mean in response to thrombocytopenia

A

enhanced thrombopoiesis

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18
Q

what can cause spuriously increased MPV

A
  • platelet aggregates
  • storage of blood at 5C
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19
Q

what is the main problem with MPV determinations

A

inaccurate when platelet activation and aggregation is present

Other problems
- MVP may not be reported when thrombocytopenia is severe or histogram shape is abnormal
- anticoagulant used and storage conditions may result in changes of MPV

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20
Q

what is buccal bleeding time used for

A
  • primarily used as a platelet function test

generally <4 min in dogs and <3 mins in cats (less reliable in horses)

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21
Q

what can cause a false positive antiplatelets antibody test

A
  • increased surface Ab following storage
  • immune complexes may be absorbed to platelets
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22
Q

how does antiplatelet antibody assays work

A

flow cytometry that detect the natural antibodies (Ab) in the platelets surface

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22
Q

what is the problem with buccal bleeding time

A
  • no value of significant thrombocytopenia is present
  • imprecise with repeat bleeding times varying by as much as 2 mins
23
Q

what is different about cat platelets

A
  • larger with higher mean platelet volume (MPV)
  • especially sensitive to activation during blood sample collection
24
Q

platelet morphology

A

photo

25
Q

macroplatelets

A
26
Q

what is the first thing you do when you get a marked thrombocytopenia on blood work

A

examine a blood film

27
Q

when does spontaneous hemorrhage from thrombocytopenia alone generally occur

A

does not occur unless platelet counts are below 25,000/uL

28
Q

what should you consider if spontaneous bleeding occurs with platelet counts above 25,000/uL

A

DIC

29
Q

what is the pathogenesis of thrombocytopenia

A
  • decreased platelet production
  • increased platelet utilization
  • increased platelet destruction
  • sequestration of platelets (spleen)
  • massive hemorrhage
  • inherited macrothrombocytopenias in dogs
30
Q

list causes of decreased platelet production

A
  • myelophthisis
  • myeloid neoplasms
  • aplastic anemia
  • chronic Ehrlichiosis infection
  • a megakaryocytic thrombocytopenia
  • inherited cyclic hematopoiesis
31
Q

what are the biggest causes of increased platelet utilization

A

DIC and thrombosis ***

32
Q

what are some other reasons that platelet utilization can be increased

A
  • vasculitis, hemangiosarcoma in dogs, and other disorders resulting in vessel injury
  • platelet aggregation can be induced by inflammatory cytokines such as platelet activating factor (PAF)
  • some snake venoms induce platelet activation and aggregation
33
Q

list what can cause increased platelet destruction

A
  • primary immune-mediated (autoimmune) thrombocytopenia, most common in dogs
  • infectious agents (bacterial, viral, protozoal, fungal) may induce vascular injury, immune-complex absorption, and direct platelet effects
    *** Tick-borne diseases including babesia, ehrlichia, anaplasma, cytauxzoon
  • secondary immune-mediated thrombocytopenia’s (drugs, infectious agents, neoplasia, SLE)
  • neonatal alloimmune thrombocytopenia (rare in pigs, horses and mules)
  • intravenous heparin (mild in horses)
  • activation of macrophages (GM-CSF, M-CSF)
34
Q

when are platelets sequestered

A

splenomegaly and hypothermia

35
Q

what is it called when splenomegaly results in permanent removal of platelets

A

hypersplenism

36
Q

platelet counts seldom decrease below —— due to hemorrhage alone

A

100,000/uL

  • counts as low as 60,000/uL have been recorded in dogs with massive hemorrhage secondary to anticoagulant rodenticide poisoning
37
Q

what is more likely present if an animal is transfused with stored blood following hemorrhage

A

thrombocytopenia

38
Q

what are some breeds of dogs that are prone to hereditary macrothrombocytopenias

A
  • cavalier king Charles spaniels (common defect)
  • Norfolk and cairn terriers
  • American akita dogs
    also may-hegglin anomaly in pugs (also has neutrophil inclusions)

^^^^ no bleeding problems in above disorders (platelets mass in blood is normal)

bernard-soulier syndrome in cocker spaniels have mucosal bleeding

39
Q

what are some clinical signs of platelet function defects

A
  • unexplained superficial bruising of skin
  • tendency for mucosal surface bleeding
  • prolonged post-traumatic hemorrhage
40
Q

what is seen in lab findings with platelet function defects

A

** prolonged bleeding time
- normal platelet counts, usually
- normal platelet morphology, usually
- normal coagulation test

41
Q

acquired platelet function defects

A
42
Q

hereditary platelet function defects

A
43
Q

what is bernard-Soulier syndrome

A

an inherited platelet adhesion defect – defect in GPIX (GP9) gene

  • in cocker spaniel dogs
  • macrothrombocytopenia (increased MPV)
  • mucosal bleeding disorders (epistaxis, hematuria, gingiva, vulva after mating)
  • prolonger buccal mucosal bleeding time
44
Q

what is glanzmann’s thrombasthenia

A

a GPIIb/IIIa deficiency in otterhounds and great pyrenees

45
Q

what are the 2 signaling pathway defects in GPIIb/IIIa activation and what breeds of dog do they affect

A

CalDAG-GEFI defect in basset hound, eskimo spitz, landseer dogs

kindlin-3 deficiency in german shepherds

46
Q

what are dense granule deficiencies

A

inherited platelet aggregation defects
- american cocker spaniels (ADP deficiency)
- chediak-higashi syndrome in cats (complete lack of dense granules)

47
Q

what breed of dog is prone to ADP receptor P2Y12 defect (inherited platelet aggregation defect)

A

greater swiss mountian dog

48
Q

are the signs of platelet procoagulant activity (PF3) defect in german shepherds

A

epistaxis, prolonged bleeding with cutaneous bruising after surgery, hyphema, intramuscular hematomas

49
Q

what do you see on blood test with platelet procoagulant activity (PF3) defect

A

standard platelet function tests (mucosal bleeding time, clot retraction, and platelet aggregation and secretion) and coagulation tests (PT, APTT, ACT) are normal

50
Q

what is platelet procoagulant activity (PF3) defect in german sheps

A

A defect in translocation and exposure of phosphatidylserine on the platelet surface, resulting in impaired coagulation in vivo

51
Q

what is enhance platelet functions

A

activated or hyperactive platelets

52
Q

list some reasons for enhanced platelet functions

A
  • diabetes mellitus
  • nephrotic syndrome
  • EPO treatment
  • FIP virus
  • heartworm DZ
  • allergic respiratory disease
53
Q

what is von Willebrand disease (vWD)

A

a quantitative and sometimes qualitative defects in plasma vWF

a defect in platelet adhesion resulting in prolonged bleeding times

common in dogs

54
Q

what breed is most frequently affected with vWD

A

Doberman pinschers

55
Q

list some reasons for thrombocytosis

A
  • some chronic inflammatory conditions
    ——– increased production of thrombopoietin (TPO) by inflammatory cytokines, especially IL-6
  • ongoing hemorrhage, especially if iron deficiency is present
  • some hemolytic anemias
  • rebound response to thrombocytopenia
  • within one week following splenectomy
  • primary thrombocytosis is a myeloproliferative neoplasm (MPN) called thrombocythemia
56
Q

primary thrombocytosis is a myeloproliferative neoplasm (MPN) called what

A

thrombocythemia

clinical pathology (18 decks)

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