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Clinical Pathology > UNIT 1 - Lecture 12: Platelets > Flashcards

UNIT 1 - Lecture 12: Platelets Flashcards

1
Q

What are tests for primary hemostasis?

A
  1. CBC with plt count and blood smear
  2. Buccal mucosal bleeding time (BMBT)
  3. vWF
  4. Plt function tests (uncommon)
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2
Q

Why should we check for plt clumping?

A

Can artifactually lower both the automated plt count and the plt estimate to unknown extent

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3
Q

What plt parameters are measured on an automated instrument?

A

Plt #, MPV, plateletcrit, PDW

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4
Q

What is MPV?

A

mean platelet volume

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5
Q

What does a low MPV mean?

A

It is of no diagnostic relevance

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6
Q

What can artifactually increase MPV?

A

Prolonged storage of blood, clumping

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7
Q

What can be a physiologic cause of increased MPV?

A

Cats - have more plt size variability

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8
Q

What can be some pathophysiologic causes of increased MPV?

A
  1. Increased production/regeneration
  2. Congenital macrothrombocytopenia
  3. Hematopoietic neoplasia
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9
Q

What is plateletcrit?

A

Reflects plt mass

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10
Q

What is PDW?

A

platelet distribution width;

Index of variability in size of plts in sample

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11
Q

What can cause an increased PDW?

A

Variation in plt size (i.e. giant plts)

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12
Q

What are some causes for plt clumping?

A
  1. Poor/challenging venipuncture
  2. Improper handling of blood sample
  3. Refrigeration of sample
  4. EDTA-induced pseudothrombocytopenia
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13
Q

What is the anticoagulant of choice for mammalian CBCs?

A

EDTA

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14
Q

What is the anticoagulant of choice for reptile (esp. chelonian) CBCs?

A

heparin

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15
Q

Where on the blood smear should you look for plt clumps?

A

feathered edge

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16
Q

What are giant plts associated with?

A

Increased MPV

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17
Q

When are giant plts produced and what does this suggest?

A

In response to thrombocytopenia;

Suggests that marrow may not be responding or that it is very early

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18
Q

Cat platelets are more _____ than dog plts.

A

reactive

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19
Q

Cat plts have a high degree of _____ normally (in health).

A

size variation

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20
Q

T/F: Giant plts are a common finding in feline blood with or without decreased plts.

A

True

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21
Q

When should you use BMBT to assess plt function?

A

Patient has adequate plt #s but questionable function

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22
Q

What are limitations to using BMBT?

A
  1. High variability
  2. Not specific
  3. Does not assess coagulation
  4. Not predictive of sx hemorrhage
  5. Subjective
  6. Poor repeatability
23
Q

When is BMBT prolonged?

A
  1. Thrombocytopenia (<90K per microliter)
  2. Thrombopathia
  3. von Willbrand’s disease
  4. Anemia
24
Q

What are 4 ways by which vWF can be measured?

A
  1. Measurement of Ag
  2. Qualitative multimeric analysis
  3. Functional assays
  4. Genetic assays
25
What is the most common method used to quantitate vWF?
Ag measurement
26
What does multimeric analysis of vWF do?
Evaluates multimeric structure of vWF - is important in distiguishing the TYPES of vWD
27
When would a genetic assay be used to test for vWF?
Only recommended for detection of carriers (does not correlate with potential for bleeding)
28
What do you call a low plt count?
thrombocytopenia
29
What do you call an increased plt count?
thrombocytosis
30
What are 3 artifactual cuases of thrombocytopenia?
1. Plt activation with collection (clumping) 2. Large plts 3. EDTA-induced pseudothrombocytopenia (rare)
31
What is the most common cause for plt-related bleeding problems?
Acquired thrombocytopenia
32
What are the 5 general causes of acquired thrombocytopenia?
1. Decreased production in marrow 2. Increased consumption or use 3. Increased destruction 4. Sequestration in spleen 5. Dilution
33
What is the relationship between thrombocytopenia and hemorrhage?
A severe thrombocytopenia is more likely to be the cause of hemorrhage than to have resulted from hemorrhage
34
What is primary immune-mediated thrombocytopenia (ITP)?
Immune-mediated destruction of plts, diagnosis of exclusion
35
What is secondary ITP due to?
Infectious agents, viral infections, drugs, neoplasia, transfusions
36
What causes neonatal thrombocytopenic purpura?
Maternal Ab from colostrum targets paternal epitopes on neonate plts in circulation and mediate plt destruction
37
What breed is likely to have congenital macrothrombocytopenia?
Cavalier King Charles Spaniel (30-50%)
38
What is congenital macrothrombocytopenia?
Defect in ß1-tubulin gene - Cannot recruit tubulin for plt formation from megas - See **giant plts, high MPV** - Low plt #
39
What is signficant about plts of greyhounds and sighthounds?
Have lower plt counts compared to other breeds (\>100K), but no clinical bleeding problems
40
What can artifactually cause thrombocytosis?
1. Automated instruments may count RBC fragments or cytoplasmic fragments 2. Lipemia 3. Bacteria or cryoglobulins
41
What is primary essential thrombocytosis?
Chronic myeloproliferative disease (neoplasia) that is rare, indolent, and a diagnosis of exclusion. (Results in persistent, marked increased plt #s)
42
What can cause secondary thrombocytosis?
1. Drugs 2. Reactive 3. Cushing's 4. Exercise/excitement 5. Recovery from thrombocytopenia 6. Post-splenectomy
43
What is bicytopenia?
Decreases in 2 cell lines
44
What is pancytopenia?
Decreases in all 3 cell lines
45
What are causes of acquired plt function disorders?
1. Neoplasia 2. Drug exposure 3. uremia 4. DIC 5. Liver disease 6. Infectious diseases 7. Secondary to marked hyperglobulinemia
46
What would lead you to suspect an inherited plt function disorder if they are uncommon?
Young patient with clinical bleeding, normal plt #s, normal vWF, normal coag panel, +/- prolonged BMBT
47
Increased plt function may predispose animals to \_\_\_\_\_.
thrombosis
48
Increased plt function is observed in dogs with what 3 conditions?
1. Lymphoma (LSA) 2. Nephrotic syndrome 3. Infectious agents (RMSF, heartworms)
49
What is the most common inherited bleeding disorder in dogs?
von Willebrand Disease
50
What CBC/test results would be expect with vWD?
BMBT prolonged, normal plt #s, normal coag values
51
What tests do we use to look for vWD and which is the most common?
1. Antigen measurement = **most common** 2. Multimeric analysis 3. Functional assays 4. Genetic assays
52
T/F: There is just 1 type of vWD
False; there are 3
53
What type of vWD the most common?
Type I (\>95% of cases)

Clinical Pathology (22 decks)

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