platelet evaluation Flashcards
Platelets look like
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
Mammalian platelet morphology
Pale blue cytoplasm counting varying amounts of pink granules
Morphology is basically the same between species, but there are some differences
Canine platelets look like
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
Feline platelets look like
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
Equine platelets look like
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
Bovine platelets look like
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
How to find platelets in a blood smear
If you are having a difficult time finding platelets, scan the feathered edge of the smear to check for aggregates (clumping)
Platelet clumping is
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
Giant platelets look like
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
Thrombocytopenia means
a decrease in the circulating platelet mass
Thrombocytosis means
is an increase in the circulating platelet mass
Thrombopathia means
an alteration in platelet function
Platelet evaluation may include
Platelet count (at least an estimate)
Platelet indices
Platelet function test
When would you do a platelet function test
Platelet function tests would be indicated when there is epistaxis, petechiae or unexplained haemorrhages
These tests are used to evaluate for evidence of thrombopathia
Platelet enumeration is
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
Platelet estimate is and how to preform
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
How to estimate platelet evaluation
of platelets in 5 oil immersion fields/5 x20 = xxx X 10^9 platelets/L
When should you perform an actual count
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
Platelet indices
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
Mean platelet volume
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
What does a high mean platelet volume mean
A high MPV value in dogs tells us there is an adequate bone marrow response
What does a low or normal MPV mean
Low or normal MPV in dogs is not significant and doesn’t give us any additional information
plateletcrit/thrombocrit (PCT) is
Is the percentage of the total blood volume that is made up of platelets
Similar to packed cell volume
Usefulness is UNKNOWN
Platelet distribution width (PDW)
Assesses the variation in platelet size
Often reported using a histogram
Usefulness is LIMITED
Platelet function tests
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
What platelet tests may a lab do
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
