Platelets Flashcards
How does EDTA affect clotting?
Cheylates Calcium altering platelet activation
What is secreted from platelets that attracts more platelets?
von Willebrand Factor
What is an appropriate estimate of PLT concentration on blood smears?
7-10 PLTs per hpf
Horses - 4-7
What are some of the granular products secreted during platelet activation?
ADP, Factors 5 and 8, thromboxane A2, calcium, vWF
What are the laboratory tests utilized to determine platelet concentration and morphology?
Blood smear, hematology analyzers
Modified-live vaccination can cause what?
When would we see this?
What should we avoid if possible?
May induce an immune response against PLTs leading to aggregation and clearance
If this happens it is 3-10 days post vaccination
Avoid surgery during this post vaccination period
What is considered normal clotting time for BMBT?
Depends on species
Dogs - 2-4 minutes
Cats - 1-3 minutes
Horses and cattle - 8-10 minutes
What is the main thing that happens during secondary hemostasis?
Deposition of fibrin
Is calcium required for platelet aggregation?
Yes dummy that’s why EDTA fucks with it
True or false:
Patients with vWD will have normal platelet counts and a prolonged BMBT
True
What happens to a platelet when it changes shape?
What is the stimulation for PLT shape change?
Shift from smooth discs to spheres with many filopodia increasing surface area
Occurs in response to thrombin
True or false:
Platelet aggregation is a reversible process.
False it is irreversible
In which species will you see more variation of platelet size normally?
Cats
What are three platelet related causes of hemorrhage?
Decreased platelet number or loss of platelet function
Decreased coagulation factor number or loss of factor function
Increased fibrinolysis
When performing a BMBT does the size of your incision make a difference?
Yes, size always matters…
What level of thrombocytopenia would be seen with hemorrhage?
Typically none, maybe mild if hemorrhage is acute and severe
What are the 3 phases of vessel injury repair utilizing platelets?
Platelet plug formation
Coagulation
Fibrinolysis
Formation of primary hemostatic plug takes how long?
How does this happen?
~3-5 minutes
Platelets adhere to subendothelium
Undergo activation
Aggregate to form a platelet plug
What are the 6 mechanisms of thrombocytopenia?
Decreased Production Destruction Sequestration Loss Consumption Pseudothrombocytopenia
What are the two causes of increased thrombus formation?
What is the pathology of this?
Where does this most commonly occur
Increased procoagulant activity
Decreased fibrinolysis
Excessive thrombus formation –> obstructed blood flow –> local hypoxia
Microvasculature
In what species are you especially concerned with and check for platelet clumping?
CATS
What is platelet consumption?
Utilization of platelets during coagulation
What will you see with decreased platelet numbers in regards to TPO?
What is a consequence of this?
With increased BM stimulation what will be seen?
Increased TPO free in plasma.
Increased bone marrow stimulation
Increased number, size, and ploidy of megakaryocytes with decreased maturation time
What is a primary neoplasm that can affect platelet production?
Leukemia
Bleeding time tests will be abnormal when?
Decreased platelet function
and/or
Decreased platelet numbers
If a macrothrombocytosis is seen on blood smear what hematology analyzer finding would you expect to see?
Increased MPV
How do you differentiate megakaryocytes microscopically?
What is a polyploid nucleus?
Large cells with abundant cytoplasm that have polyploid nucleus
Many copies of cellular DNA
What is the purpose of bleeding time tests?
What does it NOT test?
Test the ability of PLTs to form platelet plug
Does not test ability to make fibrin plug
What does an increased MPV suggest?
Increased thrompoiesis
What are causes of a reactive thrombocytosis?
Underlying disease: Neoplasia Inflammation (immune-mediated) Endocrine disease (esp. cushings) Regenerative anemias
What characteristics of platelets might alter the hematology analyzer count?
Macroplatelets or platelet clumping
True or false:
Thrombocytopenia is a specific disease.
False it is a diagnostic problem
What are causes of pseudothrombocytopenia?
Macrothrombosis or platelet clumping
What are two processes resulting in platelet destruction?
Immune-mediated thrombocytopenia (ITP)
Alloimmune thrombocytopenia
Patients are at risk for spontaneous hemorrhage when the platelet count is what?
(THIS IS SAMPLE NOT THRALL, YES THEY HAVE DIFFERENT OPINIONS ON THIS)
<30,000 / ul
What are 3 possible causes of decreased thrombocyte production?
Neoplasia
Necrosis or fibrosis of bone marrow
Bone marrow hypoplasia
Define hemostasis
Stoppage of blood
Do you typically see primary or secondary thrombocytosis?
Secondary
Primary is a unicorn diagnosis
When will you see a rebound thrombocytosis?
Following acute plt loss:
Post splenectomy
Managed (treated) ITP
The spleen retains what quantity of platelets in normal patients?
1/3 of the platelets in the body
How long does a platelet take to mature from a megakaryocyte?
4-5 days
What level of thrombocytopenia would be seen in a sequestration disorder?
Mild to moderate
What are the three steps of platelet activation?
Shape change
Flip of PLT membranes
Secretion of granule products
Will you see megakaryocytes in peripheral blood?
No, only on BMAs
Where is thrombopoietin (TPO) continually produced?
What does TPO bind to?
Liver, kidney, muscle
Receptors on platelets
What is attracted to the cell by flipping the membrane?
Calcium
What are the tests utilized to determine platelet function?
Bleeding time tests
Specific platelet function tests (TEG and Platelet mapping)
What is the approximate lifespan of a platelet?
5-10 days (shorter in cats)
Can a BMBT differentiate between Thrombocytopenia an thrombocytopathy?
No, no it can’t
Which step of primary hemostasis requires von Willebrand Factor?
What does vWF bind to on the platelet?
What is the primary function of vWF?
Adhesion
GP1b
Bridge between PLTs and collagen
True or false:
The degree of thrombocytopenia depends on the extent of bone marrow disease
True
You see an increased number of enlarged PLTs on a smear, what is this suggestive of?
Active production of platelets
What are the three steps of primary hemostasis?
Adehere
Activation
Aggregation
How do you differentiate macroplatelets microscopically?
They are as large as (or larger than) RBCs
What is the order of events in platelet plug formation?
Adhesion –> Activation –> Aggregation
What is the test for platelet production?
Bone marrow aspirate
True or false:
Animals with thrombocytosis are usually clinical in presentation.
False, they are usually asymptomatic
When would we see sequestration of platelets?
Splenomegaly, splenic torsion, neoplasia, portal hypertension, vasodilation in endotoxic shock, severe hypothermia
What is the cause of alloimune thrombocytopenia?
Who does this affect
Dam produces antiplatelet antibody from a previous pregnancy
Foals and piglets (mainly piglets)
What would be seen on CBC with ITP?
PT/PTT?
What would we see on BMA?
Severe thrombocytopenia
+/- acute hemorrhagic anemia
+/- leukocytosis
PT/PTT - Normal
Increased megakaryocytes
True or false:
Piglets with alloimmune thrombocytopenia develop fine
False!
High mortality rate from hemorrhage in piglets
What are the acquired causes of qualitative plt disorders?
Uremia
Drugs - NSAIDs, Calcium channel blockers
Fibrin Degredation Products (DIC)
Paraproteins
What things suggest PLT regeneration?
Macroplatelets on smear
Increased MPV
Increased megakaryocytes on BMA
What are characteristics of a platelet-associated bleeding pattern?
Mucosal bleeding Petechiation Ecchymosis Spontaneous hemorrhage \+/- hemorrhagic anemia
When will you see thrombocytosis in horses?
Splenic contraction
That shit is muscular as hell and gets contracted frequently after exercise
Which type of vWF is a quantitative deficiency?
Which is more severe?
Types 1 and 3
Type 3
What is the inherited plt disorder we are most concerned with?
von Willebrand’s disease
Where is vWF stored?
Weibel-Palade bodies
Probably no important but that’s a funny name
What is a consequence of vWD?
Decreased platelet adhesion
What are the two primary functions of vWF?
Platelet adhesion
Factor VIII carrier
