platelet evaluation

Question 1

Platelets look like

Answer 1

Mammalian platelets do not have a nucleus, therefore they are not a true cell
They are cytoplasmic fragments of megakaryocytes
Bird, reptile and amphibian platelets contain a nucleus, therefore they are considered true cells
Important component of hemostasis

Question 2

Mammalian platelet morphology

Answer 2

Pale blue cytoplasm counting varying amounts of pink granules
Morphology is basically the same between species, but there are some differences

Question 3

Canine platelets look like

Answer 3

Vary in size and shape
Usually small, roundich, with a distinct pink to purple granular cluster in the centre while the periphery is pale blue
May have long thread-like processes extending out in all directions

Question 4

Feline platelets look like

Answer 4

Looks similar to canine platelets
Cigar shapes and giant platelets (similar in size to RBC) are more common in cats and must be reported
How might this affect automated analyzer results
Have a higher RBC count and a lower platelet count because of the size of platelets
Increased tendency for platelet to clump

Question 5

Equine platelets look like

Answer 5

Indistinct
Often described as “ghostly” in appearance
Very pale and may be difficult to see
Granules are difficult to see and are few in number
Platelet counts are often low in healthy animals

Question 6

Bovine platelets look like

Answer 6

Granules are prominent
Platelets are usually small but giant forms do occur (up to RBC size)
Pseudopod-like projections may be present
Individual platelets often appear superimposed on red cells and must be differentiated from parasites
Platelet counts are often high in healthy animals

Question 7

How to find platelets in a blood smear

Answer 7

If you are having a difficult time finding platelets, scan the feathered edge of the smear to check for aggregates (clumping)

Question 8

Platelet clumping is

Answer 8

Clumping is common
Platelet clumps are larger and are “sticky”
When the smear is made, the clumps get pushed to the feathered edge
Clumping is to be reported
Sometimes clumps are so numerous and/or large that platelet counts are not accurate

Question 9

Giant platelets look like

Answer 9

Also known as megathrombocytes
Can be bigger than red blood cells (especially in cats)
Giant cigar shaped and other oddly shaped platelets should be noted on the report
Giant platelets may affect the total RBC and platelet counts generated by automated analyzers

Question 10

Thrombocytopenia means

Answer 10

a decrease in the circulating platelet mass

Question 11

Thrombocytosis means

Answer 11

is an increase in the circulating platelet mass

Question 12

Thrombopathia means

Answer 12

an alteration in platelet function

Question 13

Platelet evaluation may include

Answer 13

Platelet count (at least an estimate)
Platelet indices
Platelet function test

Question 14

When would you do a platelet function test

Answer 14

Platelet function tests would be indicated when there is epistaxis, petechiae or unexplained haemorrhages
These tests are used to evaluate for evidence of thrombopathia

Question 15

Platelet enumeration is

Answer 15

Most often done using automated analyzers
Can be very inaccurate due to:
Platelet clumping
Similarity in size to red blood cells–especially problematic in cats
Need to use a fresh EDTA blood sample
Make sure that there are no clots

Question 16

Platelet estimate is and how to preform

Answer 16

The platelet estimate is performed by examining the blood smear in the monolayer region
Estimates should always be done as part of the quality control for your machines
Count a minimum of 5 oil immersion fields of view
A normal patient will have between 7-10 platelets/hpf

Question 17

How to estimate platelet evaluation

Answer 17

of platelets in 5 oil immersion fields/5 x20 = xxx X 10^9 platelets/L

Question 18

When should you perform an actual count

Answer 18

An actual count should be performed when estimates are lower than:
Canine:<200 x 10⁹/L
Feline:<300 x 10⁹/L
Large Animals: <100 x10⁹/L

Question 19

Platelet indices

Answer 19

Performed by many automated analyzers
Platelet indices include:
Mean platelet volume (MPV)
Plateletcrit (PCT)
Platelet distribution Width (PDW)
The usefulness of the platelet indices is not well documented for veterinary species

Question 20

Mean platelet volume

Answer 20

This is the average size of the individual platelets counted by the analyzer
Mathematically calculated
Measured in femtoliters (fL)
Not useful for feline or Cavalier King Charles Spaniel patients
Platelets will swell when exposed to EDTA–run samples and make slides as soon as possible after collection to minimize artifact
Anticoagulants can affect results

Question 21

What does a high mean platelet volume mean

Answer 21

A high MPV value in dogs tells us there is an adequate bone marrow response

Question 22

What does a low or normal MPV mean

Answer 22

Low or normal MPV in dogs is not significant and doesn’t give us any additional information

Question 23

plateletcrit/thrombocrit (PCT) is

Answer 23

Is the percentage of the total blood volume that is made up of platelets
Similar to packed cell volume
Usefulness is UNKNOWN

Question 24

Platelet distribution width (PDW)

Answer 24

Assesses the variation in platelet size
Often reported using a histogram
Usefulness is LIMITED

Question 25

Platelet function tests

Answer 25

Used to assess for evidence of thrombopathia
Automated analyzers in the clinic test the ability of the platelets to aggregate and secrete platelet factors
Idexx’s Coag Dx
Manual Test
Buccal Mucosal Bleeding Time

Question 26

What platelet tests may a lab do

Answer 26

Reticulated platelet count
-These are newly released platelets
-Equated to red blood cell reticulocytes in that they both indicate a bone marrow response
Antiplatelet antibody assays
-Evaluate for the presence of antibodies on the surface of platelets