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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
Q

What is the most common method used to quantitate vWF?

A

Ag measurement

26
Q

What does multimeric analysis of vWF do?

A

Evaluates multimeric structure of vWF - is important in distiguishing the TYPES of vWD

27
Q

When would a genetic assay be used to test for vWF?

A

Only recommended for detection of carriers (does not correlate with potential for bleeding)

28
Q

What do you call a low plt count?

A

thrombocytopenia

29
Q

What do you call an increased plt count?

A

thrombocytosis

30
Q

What are 3 artifactual cuases of thrombocytopenia?

A
  1. Plt activation with collection (clumping)
  2. Large plts
  3. EDTA-induced pseudothrombocytopenia (rare)
31
Q

What is the most common cause for plt-related bleeding problems?

A

Acquired thrombocytopenia

32
Q

What are the 5 general causes of acquired thrombocytopenia?

A
  1. Decreased production in marrow
  2. Increased consumption or use
  3. Increased destruction
  4. Sequestration in spleen
  5. Dilution
33
Q

What is the relationship between thrombocytopenia and hemorrhage?

A

A severe thrombocytopenia is more likely to be the cause of hemorrhage than to have resulted from hemorrhage

34
Q

What is primary immune-mediated thrombocytopenia (ITP)?

A

Immune-mediated destruction of plts, diagnosis of exclusion

35
Q

What is secondary ITP due to?

A

Infectious agents, viral infections, drugs, neoplasia, transfusions

36
Q

What causes neonatal thrombocytopenic purpura?

A

Maternal Ab from colostrum targets paternal epitopes on neonate plts in circulation and mediate plt destruction

37
Q

What breed is likely to have congenital macrothrombocytopenia?

A

Cavalier King Charles Spaniel (30-50%)

38
Q

What is congenital macrothrombocytopenia?

A

Defect in ß1-tubulin gene

  • Cannot recruit tubulin for plt formation from megas
  • See giant plts, high MPV
  • Low plt #
39
Q

What is signficant about plts of greyhounds and sighthounds?

A

Have lower plt counts compared to other breeds (>100K), but no clinical bleeding problems

40
Q

What can artifactually cause thrombocytosis?

A
  1. Automated instruments may count RBC fragments or cytoplasmic fragments
  2. Lipemia
  3. Bacteria or cryoglobulins
41
Q

What is primary essential thrombocytosis?

A

Chronic myeloproliferative disease (neoplasia) that is rare, indolent, and a diagnosis of exclusion.

(Results in persistent, marked increased plt #s)

42
Q

What can cause secondary thrombocytosis?

A
  1. Drugs
  2. Reactive
  3. Cushing’s
  4. Exercise/excitement
  5. Recovery from thrombocytopenia
  6. Post-splenectomy
43
Q

What is bicytopenia?

A

Decreases in 2 cell lines

44
Q

What is pancytopenia?

A

Decreases in all 3 cell lines

45
Q

What are causes of acquired plt function disorders?

A
  1. Neoplasia
  2. Drug exposure
  3. uremia
  4. DIC
  5. Liver disease
  6. Infectious diseases
  7. Secondary to marked hyperglobulinemia
46
Q

What would lead you to suspect an inherited plt function disorder if they are uncommon?

A

Young patient with clinical bleeding, normal plt #s, normal vWF, normal coag panel, +/- prolonged BMBT

47
Q

Increased plt function may predispose animals to _____.

A

thrombosis

48
Q

Increased plt function is observed in dogs with what 3 conditions?

A
  1. Lymphoma (LSA)
  2. Nephrotic syndrome
  3. Infectious agents (RMSF, heartworms)
49
Q

What is the most common inherited bleeding disorder in dogs?

A

von Willebrand Disease

50
Q

What CBC/test results would be expect with vWD?

A

BMBT prolonged, normal plt #s, normal coag values

51
Q

What tests do we use to look for vWD and which is the most common?

A
  1. Antigen measurement = most common
  2. Multimeric analysis
  3. Functional assays
  4. Genetic assays
52
Q

T/F: There is just 1 type of vWD

A

False; there are 3

53
Q

What type of vWD the most common?

A

Type I (>95% of cases)

Clinical Pathology (22 decks)

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