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
2
Q
What is the lifespan of a platelet?
A
5-10 days
3
Q
Where is 1/3 of platelets located?
A
spleen
4
Q
What are the presence of macroplatelets suggestive of?
A
increased platelet production
5
Q
What is the precursor to platelets?
A
Megakaryocytes
6
Q
What regulates megakaryocyte production and differentiation?
A
Thrombopoietin
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
8
Q
What do you use to test Platelet concentration and morphology?
A
Blood smear
Hematology analyzer
9
Q
What do you use to test function of platelets?
A
Bleeding time tests
Specific platelet function tests
10
Q
What do you use to test production of platelets?
A
Bone marrow aspirate
11
Q
What do you use to test anti-platelet antibodies?
A
Platelet surface assocaited immunoglobulin (PSAIg)
Immunofluorescent antimegakaryocytic antibody test
12
Q
Below what interval is Thrombocytopenia severe?
A
13
Q
Below what interval would you have spontaneous hemorrhage?
A
14
Q
What does MPV stand for?
A
Mean Platelet Volume
15
Q
What does an increased MPV suggest?
A
increased thrombopoiesis
16
Q
What does an increased number of enlarged platelets suggest?
A
active production of platelets
17
Q
In thrombocytopenia, free TPO should be….
A
Increased
18
Q
If TPO is increased and the bone marrow is healthy, you expect to see…
A
Increased megakaryocyte numbers with increased ploidy
19
Q
What 3 things suggest platelet regeneration?
A
Macroplatelets on theh blood smear
Increased MPV
Increased megakaryocyte numbers
20
Q
What are you evaluating on a bone marrow aspirate?
A
megakaryocyte number and morphology
21
Q
A prolonged BMBT (Buccal mucosal bleeding time) can be caused by:
A
decreased number of platelets
22
Q
What are the Clinical features of Thrombocytopenia?
A
Mucosal bleeding Petechiation Ecchymosis Spontanous hemorrhage hemorrhagic anemia
23
Q
What are the mechanisms of Thrombocytopenia?
A
Production Destruction Sequestration Loss Consumption
24
Q
What is the mechanism for decreased production?
A
Bone marrow hypoplasia
Neoplasia
Myelonecrosis or Myelofibrosis
25
The degree of thrombocytopenia depends on....
the extent of bone marrow disease
26
What is the mechanism for destruction of platelets?
Immune mediated thrombocytopenia
Alloimmune thrombocytopenia
Modified live vaccination
27
What is Alloimmune thrombocytopenia?
Dam produces antiplatelet antibodies from previous pregnancy
28
What are the two types of immune mediated thrombocytopenia?
Primary
| Seconday
29
What is primary immune mediated thrombocytopenia?
Idiopathic
30
What is secondary immune mediated thrombocytopenia?
Drugs
Viruses
Sepsis
Neoplasia
31
How does a modified live vaccination cause thrombocytopenia?
Induces an immune response against platelets --> platelet aggregation --> clearance
32
What are the clinical signs for destructive thrombocytopenia?
Bleeding from the mucosal membranes
petechiation
Ecchymosis
+/- anemia
33
Platelet counts in patients with immune mediated thrombocytopenia are typically...
Severely decreased
34
What kind of thrombocytopenia will you see with sequestration of platelets?
Mild to moderate thrombocytopenia
35
When you would you see sequestration of platelets?
```
Splenomegaly
Splenic torsion
neoplasia
Hepatomegaly
portal hypertension
vasodilation in endotoxic shock
severe hypothermia
```
36
What kind of thrombocytopenia would you see with hemorrhage?
Normal to Mild thrombocytopenia
37
What causes consumption of platelets?
DIC
Vasculitis
Viral infection
38
When does pseudothrombocytopenia happen?
Macroplatelets
| Clumped platelets
39
On a blood smear marked macrothrombocytosis is observed. This finding correlates with:
Increased MPV
40
What is thrombocytosis?
Increased concentration of platelets
41
What are the 2 major mechanisms of thrombocytosis?
Increased production
| Increased distribution in plasma
42
what is a primary cause of Thrombocytosis?
Neoplasia
43
What is a secondary cause of thrombocytosis?
Chronic inflammatory disease
Iron deficiency anemia
Chronic hemorrhage
IMHA
44
What other causes can cause thrombocytosis?
```
Rebound from thrombocytopenia
Response to some drugs
Post-splenectomy
Excitment and exercise
Splenic contraction
```
45
Hemostasis
Stoppage of blood
46
What causes the formation of a thrombus?
increase procoagulant activity
| decreased fibrinolysis
47
What causes hemorrhage?
decreased procoagulant activity
decreassed platelet number or loss of platelet function
Increased fibrinolysis
48
What is primary hemostasis?
the formation of a primary hemostatic plug
49
What are the steps of Primary Hemostasis?
Adherence --> Activation --> Aggregation
50
What factor is used to bind GP1b to platelet surface?
von Willebrands Factor
51
What are the factors required for activating the platelet?
Calcium
ADP
Thromboxane A2
Thrombin
52
What happens to the platelet during activation?
A shape change
flipping of the membrane
spreading out to create more surface area
53
What happens when Phosphotidylserine flips to the outside of the platelet membrane?
The surface becomes negatively charged
54
What happens during activation?
Platelet plug is formed
55
What else do platelets do to aid in regeneration and repair?
They retract to pull the edges of the wound together
56
What do bleeding tests test for?
The ability of platelets to form a platelet plug
57
When is bleeding time abnormal or prolonged?
Decreased platelet function
| decreased platelet numbers
58
What diagnostic test is commonly used to assess platelet function?
Buccal mucosal bleeding time (BMBT)
59
When do you suspect a qualitative disorder in an animal?
Clinical signs of thrombocytopenia
| Normal Platelet count
60
What are the two types of qualitative disorders?
Acquired
| Inherited
61
What can cause an acquired qualitative disease?
Uremia
Drugs
Fibrin degradation products
Paraproteins
62
What can cause an inherited qualitative disorder?
Absence of glycoprotein receptors
Absence or reduction in platelet granules
Signal transduction defects
Von Willebrand disease
63
von Willebrand Disease
Defects in the adhesion molecule that binds platelets during initiation of platelet plug causing decreased platelet adhesion
64
vWF is a carrier for....
Factor VIII
65
What are the two forms of von Willebrand disease?
Quantitative deficiency
| Qualitative abnormality
66
What are the clinical signs of von Willebrands disease?
Mild to severe bleeding
67
When do signs decrease for von Willebrands disease?
with age and successive pregnancies
68
When do you suspect von Willebrands disease?
Platelet count is normal
| Buccal mucosal bleeding time is prolonged
69
What is secondary hemostasis?
Stabilization of the platelet plug via fibrin meshwork
70
Which Factor is involved in the extrinsic pathway?
Factor VII
71
Which Factors are involved in the Intrinsic pathway?
Factor XII, XI, IX, VIII ( Not $12 but $11.98!)
72
What factor is Calcium?
Factor IV
73
Where are coagulation factors synthesized?
Liver
74
What are the two types of factors involved in the coagulation cascade?
Enzymatic and Nonenzymatic
75
What converts Fibrinogen to Fibrin?
Thrombin
76
What converts Prothrombin to Thrombin?
Factor Xa with Factor Va
77
What two factors convert Factor X to Xa?
Factors IXa, VIIa, and VII with the help of Factor VIIIa
78
What converts Factor VII to VIIa?
```
Tissue Factor (III)
Factor Xa
```
79
What converts Factor IX to IXa?
Factor VIIa
80
What conversions is Tissue Factor (III) involved in?
Factor VII --> VIIa
| Factor IX --> IXa
81
What conversions is Factor Va involved in?
Prothrombin to Thrombin
82
What three phases are the cells involved with the coagulation cascade?
Initiation
Amplification
Propagation
83
What is required for the initiation of secondary hemostasis?
Tissue Factor (III)
84
What does thrombin promote?
Amplification
85
How does Thrombin promote amplification?
By feedbacking to Factors: XI, VII, VIIIa, and Va
86
What is propagation?
Thrombin is generated on the platelet surfce driving formation of Fibrin
87
What inhibits Thrombin, Factor IXa and Xa?
Antithrombin
88
How does Antithrombin work?
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
What is formed when there is excess fibrin production?
Schistocytes
90
What else helps break down Fibrin?
Plasminogen secreted by neighboring cells --> converted to Plasmin byttissue Plasminogen Activator (TPA)
91
What three things does Plasmin act on?
Fibrinogen
Soluble Fibrin
Cross linked fibrin
92
What is created when plasmin acts on soluble fibrin?
Fibrin Degradation Products
93
What is created when plasmin acts on cross-linked fibrin?
D-Dimers
94
What tests can test for Procoagulant activity?
```
Activated Partial Prothrombin time (aPTT, PTT)
Prothrombin time (PT)
Thrombin Time (TT), Fibrinogen
PIVKA
Specific factor assays
```
95
What tests can test for anticoagulant activity?
```
Fibrinolytic activity - Fibrin degradation products, D-Dimers
Inhibitor consumption (Antithrombin (AT))
```
96
What tube do you use for plasma testing?
Blue top Sodium Citrate Tube
97
What two tests are used for the Intrinsic pathway?
aPTT
| ACT
98
What test is used for the extrinsic pathway?
PT
99
What tests for Fibrinogen?
TT
100
What does aPTT stands for?
Activated partial thromboplastin time
101
What does ACT stand for?
Activated Clotting Time
102
What are the aPTT and ACT testing for?
Measure time for Fibrin clot formation
103
What is the significance of a prolonged aPTT or ACT?
Deficiency or inhibition of any intrinsic or common pathway factor
Heparin Therapy
104
What percent deficiency of factor is required before prolongation is detected in aPTT?
70%
105
What percent deficiency of factor is required before prologation is detected in ACT?
95%
106
What is the significance of prolongation in a PT?
Factor VII deficiency (Good screening for Vitamin K deficiency)
Deficiency or inhibition of common pathway factor
107
What percent deficiency of factor is required before prolongation is detected in PT?
70%
108
When does increased concentration of Fibrin Degradation products occur?
Increased Fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearnace of FDP by liver
109
When does increased concentration of D-Dimers occur?
Increased fibrinolysis
Severe internal hemorrhage with fibrinolysis
Decreased clearance of FDP by the liver
110
What causes Warfarin Toxicosis?
Poisoning with coumarin derivatives
111
How does Warfarin interfere with the clotting cascade?
It inhibits the Vitamin K cycle causing the Factors to not become negatively charged and therefore not attracted to platelets
112
What are the clinical signs of Warfarin Toxicosis?
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
What are the laboratory features of Warfarin Toxicosis?
```
Regenerative Anemia
Variable Leukogram
Normal Platelet count
Prolonged PT, aPTT, ACT
Positive PIVKA
```
114
What is the treatment for Warfarin Toxicosis?
Decontamination
Supplement Vitamin K
Plasma and/or blood transfusions
115
What is DIC?
Disseminated Intravascular Coagulation - Depletion of the coagulation factors and platelets --> bleeding
116
What is the cause of DIC?
```
continued activation of coagulation and fibrinolysis -
Sepsis
Tissue Necrosis
Neoplasia
Proteolytic Enzymes (Snake venom)
Stagnant blood flow
```
117
What are the two phases of DIC?
Hypercoagulable
| Consumptive
118
What happens in the Hypercoagulable phase of DIC?
Thrombosis
| Ischemic necorsis and organ dysfunction
119
What happens in the consumptive phase of DIC?
Consumption of platelets, coag factors, and AT
| Bleeding!!
120
What are the clinical signs associated with DIC?
Signs of Organ Dysfunction
| Bleeding - Mucosal and Hemorrhage
121
What are the laboratory features of the consumptive phase of DIC?
```
Thrombocytopenia
Prolonged PT, aPTT
Decreased fibrinogen concentration
increased FDP and D-dimers
Decreased antithrombin (AT)
Hemorrhagic anemia
Schistocytes
```
122
What is the treatment for DIC?
Identify and eliminate the underlying disorder
Fluid therapy
Transfusion therapy
123
What is the cardinal bloodwork finding for a patient in the consumptive phase of DIC?
Thrombocytopenia
124
What is coagulopathy and liver disease?
decreased synthesis of coagulation factors
| Production of dysfunctional factors
125
What is a inherited factor deficiency?
Hemophilia A: VIII
126
What are the clinical signs of hemophilia A: VIII?
Mild, moderate, or severe bleeding
127
What are the laboratory findings for Hemophilia A: VIII?
Normal Platelet count
Prolonged aPTT and ACT
PT is normal
128
What kind of genetic disorder is Hemophilia A: VIII?
X-linked recessive in dogs and cattle
