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RUSVM Clinical Pathology 2016 > Platelets > Flashcards

Platelets Flashcards

1
Q

List characteristics of platelet morphology

A 
Small granular discs
Membrane glycoproteins that act as receptors for ligands (vWF and fibrinogen)
Anucleate
Cytoskeleton
alpha and dense granules
canalicular and tubular systems
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2
Q

What is the lifespan of a platelet?

A

5-10 days

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3
Q

Where is 1/3 of platelets located?

A

spleen

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4
Q

What are the presence of macroplatelets suggestive of?

A

increased platelet production

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5
Q

What is the precursor to platelets?

A

Megakaryocytes

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6
Q

What regulates megakaryocyte production and differentiation?

A

Thrombopoietin

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7
Q

What happens when there are decreased numbers of platelets?

A

free plasma TPO increases –> Bone marrow –> increase in number, size and ploidy of megakaryocytes

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8
Q

What do you use to test Platelet concentration and morphology?

A

Blood smear

Hematology analyzer

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9
Q

What do you use to test function of platelets?

A

Bleeding time tests

Specific platelet function tests

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10
Q

What do you use to test production of platelets?

A

Bone marrow aspirate

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11
Q

What do you use to test anti-platelet antibodies?

A

Platelet surface assocaited immunoglobulin (PSAIg)

Immunofluorescent antimegakaryocytic antibody test

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12
Q

Below what interval is Thrombocytopenia severe?

A
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13
Q

Below what interval would you have spontaneous hemorrhage?

A
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14
Q

What does MPV stand for?

A

Mean Platelet Volume

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15
Q

What does an increased MPV suggest?

A

increased thrombopoiesis

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16
Q

What does an increased number of enlarged platelets suggest?

A

active production of platelets

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17
Q

In thrombocytopenia, free TPO should be….

A

Increased

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18
Q

If TPO is increased and the bone marrow is healthy, you expect to see…

A

Increased megakaryocyte numbers with increased ploidy

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19
Q

What 3 things suggest platelet regeneration?

A

Macroplatelets on theh blood smear
Increased MPV
Increased megakaryocyte numbers

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20
Q

What are you evaluating on a bone marrow aspirate?

A

megakaryocyte number and morphology

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21
Q

A prolonged BMBT (Buccal mucosal bleeding time) can be caused by:

A

decreased number of platelets

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22
Q

What are the Clinical features of Thrombocytopenia?

A 
Mucosal bleeding
Petechiation
Ecchymosis
Spontanous hemorrhage
hemorrhagic anemia
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23
Q

What are the mechanisms of Thrombocytopenia?

A 
Production
Destruction
Sequestration
Loss
Consumption
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24
Q

What is the mechanism for decreased production?

A

Bone marrow hypoplasia
Neoplasia
Myelonecrosis or Myelofibrosis

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25
Q

The degree of thrombocytopenia depends on….

A

the extent of bone marrow disease

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26
Q

What is the mechanism for destruction of platelets?

A

Immune mediated thrombocytopenia
Alloimmune thrombocytopenia
Modified live vaccination

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27
Q

What is Alloimmune thrombocytopenia?

A

Dam produces antiplatelet antibodies from previous pregnancy

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28
Q

What are the two types of immune mediated thrombocytopenia?

A

Primary

Seconday

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29
Q

What is primary immune mediated thrombocytopenia?

A

Idiopathic

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30
Q

What is secondary immune mediated thrombocytopenia?

A

Drugs
Viruses
Sepsis
Neoplasia

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31
Q

How does a modified live vaccination cause thrombocytopenia?

A

Induces an immune response against platelets –> platelet aggregation –> clearance

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32
Q

What are the clinical signs for destructive thrombocytopenia?

A

Bleeding from the mucosal membranes
petechiation
Ecchymosis
+/- anemia

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33
Q

Platelet counts in patients with immune mediated thrombocytopenia are typically…

A

Severely decreased

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34
Q

What kind of thrombocytopenia will you see with sequestration of platelets?

A

Mild to moderate thrombocytopenia

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35
Q

When you would you see sequestration of platelets?

A 
Splenomegaly
Splenic torsion
neoplasia
Hepatomegaly
portal hypertension
vasodilation in endotoxic shock
severe hypothermia
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36
Q

What kind of thrombocytopenia would you see with hemorrhage?

A

Normal to Mild thrombocytopenia

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37
Q

What causes consumption of platelets?

A

DIC
Vasculitis
Viral infection

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38
Q

When does pseudothrombocytopenia happen?

A

Macroplatelets

Clumped platelets

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39
Q

On a blood smear marked macrothrombocytosis is observed. This finding correlates with:

A

Increased MPV

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40
Q

What is thrombocytosis?

A

Increased concentration of platelets

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41
Q

What are the 2 major mechanisms of thrombocytosis?

A

Increased production

Increased distribution in plasma

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42
Q

what is a primary cause of Thrombocytosis?

A

Neoplasia

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43
Q

What is a secondary cause of thrombocytosis?

A

Chronic inflammatory disease
Iron deficiency anemia
Chronic hemorrhage
IMHA

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44
Q

What other causes can cause thrombocytosis?

A 
Rebound from thrombocytopenia
Response to some drugs
Post-splenectomy
Excitment and exercise
Splenic contraction
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45
Q

Hemostasis

A

Stoppage of blood

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46
Q

What causes the formation of a thrombus?

A

increase procoagulant activity

decreased fibrinolysis

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47
Q

What causes hemorrhage?

A

decreased procoagulant activity
decreassed platelet number or loss of platelet function
Increased fibrinolysis

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48
Q

What is primary hemostasis?

A

the formation of a primary hemostatic plug

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49
Q

What are the steps of Primary Hemostasis?

A

Adherence –> Activation –> Aggregation

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50
Q

What factor is used to bind GP1b to platelet surface?

A

von Willebrands Factor

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51
Q

What are the factors required for activating the platelet?

A

Calcium
ADP
Thromboxane A2
Thrombin

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52
Q

What happens to the platelet during activation?

A

A shape change
flipping of the membrane
spreading out to create more surface area

53
Q

What happens when Phosphotidylserine flips to the outside of the platelet membrane?

A

The surface becomes negatively charged

54
Q

What happens during activation?

A

Platelet plug is formed

55
Q

What else do platelets do to aid in regeneration and repair?

A

They retract to pull the edges of the wound together

56
Q

What do bleeding tests test for?

A

The ability of platelets to form a platelet plug

57
Q

When is bleeding time abnormal or prolonged?

A

Decreased platelet function

decreased platelet numbers

58
Q

What diagnostic test is commonly used to assess platelet function?

A

Buccal mucosal bleeding time (BMBT)

59
Q

When do you suspect a qualitative disorder in an animal?

A

Clinical signs of thrombocytopenia

Normal Platelet count

60
Q

What are the two types of qualitative disorders?

A

Acquired

Inherited

61
Q

What can cause an acquired qualitative disease?

A

Uremia
Drugs
Fibrin degradation products
Paraproteins

62
Q

What can cause an inherited qualitative disorder?

A

Absence of glycoprotein receptors
Absence or reduction in platelet granules
Signal transduction defects
Von Willebrand disease

63
Q

von Willebrand Disease

A

Defects in the adhesion molecule that binds platelets during initiation of platelet plug causing decreased platelet adhesion

64
Q

vWF is a carrier for….

A

Factor VIII

65
Q

What are the two forms of von Willebrand disease?

A

Quantitative deficiency

Qualitative abnormality

66
Q

What are the clinical signs of von Willebrands disease?

A

Mild to severe bleeding

67
Q

When do signs decrease for von Willebrands disease?

A

with age and successive pregnancies

68
Q

When do you suspect von Willebrands disease?

A

Platelet count is normal

Buccal mucosal bleeding time is prolonged

69
Q

What is secondary hemostasis?

A

Stabilization of the platelet plug via fibrin meshwork

70
Q

Which Factor is involved in the extrinsic pathway?

A

Factor VII

71
Q

Which Factors are involved in the Intrinsic pathway?

A

Factor XII, XI, IX, VIII ( Not $12 but $11.98!)

72
Q

What factor is Calcium?

A

Factor IV

73
Q

Where are coagulation factors synthesized?

A

Liver

74
Q

What are the two types of factors involved in the coagulation cascade?

A

Enzymatic and Nonenzymatic

75
Q

What converts Fibrinogen to Fibrin?

A

Thrombin

76
Q

What converts Prothrombin to Thrombin?

A

Factor Xa with Factor Va

77
Q

What two factors convert Factor X to Xa?

A

Factors IXa, VIIa, and VII with the help of Factor VIIIa

78
Q

What converts Factor VII to VIIa?

A 
Tissue Factor (III) 
Factor Xa
79
Q

What converts Factor IX to IXa?

A

Factor VIIa

80
Q

What conversions is Tissue Factor (III) involved in?

A

Factor VII –> VIIa

Factor IX –> IXa

81
Q

What conversions is Factor Va involved in?

A

Prothrombin to Thrombin

82
Q

What three phases are the cells involved with the coagulation cascade?

A

Initiation
Amplification
Propagation

83
Q

What is required for the initiation of secondary hemostasis?

A

Tissue Factor (III)

84
Q

What does thrombin promote?

A

Amplification

85
Q

How does Thrombin promote amplification?

A

By feedbacking to Factors: XI, VII, VIIIa, and Va

86
Q

What is propagation?

A

Thrombin is generated on the platelet surfce driving formation of Fibrin

87
Q

What inhibits Thrombin, Factor IXa and Xa?

A

Antithrombin

88
Q

How does Antithrombin work?

A

Heparin binds to Antithrombin –> Heparin causes conformationa; change and exposes the thrombin binding site –> Thrommbin binds to AT=TAT complex and Heparin floats away –> the TAT complex is cleared by the phagocytic system

89
Q

What is formed when there is excess fibrin production?

A

Schistocytes

90
Q

What else helps break down Fibrin?

A

Plasminogen secreted by neighboring cells –> converted to Plasmin byttissue Plasminogen Activator (TPA)

91
Q

What three things does Plasmin act on?

A

Fibrinogen
Soluble Fibrin
Cross linked fibrin

92
Q

What is created when plasmin acts on soluble fibrin?

A

Fibrin Degradation Products

93
Q

What is created when plasmin acts on cross-linked fibrin?

A

D-Dimers

94
Q

What tests can test for Procoagulant activity?

A 
Activated Partial Prothrombin time (aPTT, PTT)
Prothrombin time (PT)
Thrombin Time (TT), Fibrinogen
PIVKA
Specific factor assays
95
Q

What tests can test for anticoagulant activity?

A 
Fibrinolytic activity - Fibrin degradation products, D-Dimers
Inhibitor consumption (Antithrombin (AT))
96
Q

What tube do you use for plasma testing?

A

Blue top Sodium Citrate Tube

97
Q

What two tests are used for the Intrinsic pathway?

A

aPTT

ACT

98
Q

What test is used for the extrinsic pathway?

A

PT

99
Q

What tests for Fibrinogen?

A

TT

100
Q

What does aPTT stands for?

A

Activated partial thromboplastin time

101
Q

What does ACT stand for?

A

Activated Clotting Time

102
Q

What are the aPTT and ACT testing for?

A

Measure time for Fibrin clot formation

103
Q

What is the significance of a prolonged aPTT or ACT?

A

Deficiency or inhibition of any intrinsic or common pathway factor
Heparin Therapy

104
Q

What percent deficiency of factor is required before prolongation is detected in aPTT?

A

70%

105
Q

What percent deficiency of factor is required before prologation is detected in ACT?

A

95%

106
Q

What is the significance of prolongation in a PT?

A

Factor VII deficiency (Good screening for Vitamin K deficiency)
Deficiency or inhibition of common pathway factor

107
Q

What percent deficiency of factor is required before prolongation is detected in PT?

A

70%

108
Q

When does increased concentration of Fibrin Degradation products occur?

A

Increased Fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearnace of FDP by liver

109
Q

When does increased concentration of D-Dimers occur?

A

Increased fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearance of FDP by the liver

110
Q

What causes Warfarin Toxicosis?

A

Poisoning with coumarin derivatives

111
Q

How does Warfarin interfere with the clotting cascade?

A

It inhibits the Vitamin K cycle causing the Factors to not become negatively charged and therefore not attracted to platelets

112
Q

What are the clinical signs of Warfarin Toxicosis?

A

Bleeding
Anemia
Hypovolemic shock
Dyspnea due to bleeding into the thoracic cavity
Lameness due to bleeding into the joints
Neurological signs due to bleed in the brain

113
Q

What are the laboratory features of Warfarin Toxicosis?

A 
Regenerative Anemia
Variable Leukogram
Normal Platelet count
Prolonged PT, aPTT, ACT
Positive PIVKA
114
Q

What is the treatment for Warfarin Toxicosis?

A

Decontamination
Supplement Vitamin K
Plasma and/or blood transfusions

115
Q

What is DIC?

A

Disseminated Intravascular Coagulation - Depletion of the coagulation factors and platelets –> bleeding

116
Q

What is the cause of DIC?

A 
continued activation of coagulation and fibrinolysis - 
Sepsis
Tissue Necrosis
Neoplasia
Proteolytic Enzymes (Snake venom)
Stagnant blood flow
117
Q

What are the two phases of DIC?

A

Hypercoagulable

Consumptive

118
Q

What happens in the Hypercoagulable phase of DIC?

A

Thrombosis

Ischemic necorsis and organ dysfunction

119
Q

What happens in the consumptive phase of DIC?

A

Consumption of platelets, coag factors, and AT

Bleeding!!

120
Q

What are the clinical signs associated with DIC?

A

Signs of Organ Dysfunction

Bleeding - Mucosal and Hemorrhage

121
Q

What are the laboratory features of the consumptive phase of DIC?

A 
Thrombocytopenia
Prolonged PT, aPTT
Decreased fibrinogen concentration
increased FDP and D-dimers
Decreased antithrombin (AT) 
Hemorrhagic anemia
Schistocytes
122
Q

What is the treatment for DIC?

A

Identify and eliminate the underlying disorder
Fluid therapy
Transfusion therapy

123
Q

What is the cardinal bloodwork finding for a patient in the consumptive phase of DIC?

A

Thrombocytopenia

124
Q

What is coagulopathy and liver disease?

A

decreased synthesis of coagulation factors

Production of dysfunctional factors

125
Q

What is a inherited factor deficiency?

A

Hemophilia A: VIII

126
Q

What are the clinical signs of hemophilia A: VIII?

A

Mild, moderate, or severe bleeding

127
Q

What are the laboratory findings for Hemophilia A: VIII?

A

Normal Platelet count
Prolonged aPTT and ACT
PT is normal

128
Q

What kind of genetic disorder is Hemophilia A: VIII?

A

X-linked recessive in dogs and cattle

RUSVM Clinical Pathology 2016 (22 decks)

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