What is hemostasis?
Stopping blood
What is the goal of hemostasis?
To sop blood without obstructing blood flow
Injury to a vessel causes these three steps.
Vessel constriction
Platelet adhesion
Activation of coagulation
What is blanaced hemostasis?
Balance between thrombosis and hemorrhage
How much of the platelet mass is in the spleen?
1/3
What does the presence of large and giant platelets suggest?
Increased platelet production
Where do you find megakaryocytes?
In the sinus in bone
How long does it take to go from megakaryoblast to platelet release?
4-5 days
How do platelets get into circulation?
Proplatelet processes extend into the sinus lumen and break into individual platelets
What substance regulates platelet production?
Thrombopoietin (TPO)
Where in TPO continually produced? (3 places)
Liver
Basement membrane
Endothelium
How does TPO work?
It binds to platelets. The less platelets, the more free plasma TPO which stimulates thrombopoiesis.
Will EPO stimulate thrombopoiesis?
Yes
What is the lifespan of a platelet?
~5-10 days (shorter in cats)
What are the two main functions of platelets?
Primary hemostasis
Support secondary hemostasis
What is primary hemostasis?
Formation of the primary hemostatic plug
How long does primary hemostasis take?
3-5 minutes
What does primary hemostasis entail?
PLTs adhere to the subendothelium, activate, secrete granules and aggregate to form a plug.
What 4 things does PLT adhesion require?
vonWillebrand Factor
ADP
Ca2+
Serotonin
What does PLT activation entail?
Shape change from smooth disc to spheres with many filapodia in response to thrombin.
During PLT activation, what doe the PLTs secrete from their granules?
Factors V and VIII
Thromboxane A2
Ca2+
What are the 4 functions of the platelet granule products?
Recruit more PLTs
Further PLT activation
Facilitate coagulation
Mediate vessel repair
Why is Calcium required for platelet aggregation?
Because the Ca2+ gives the activated PLTs a positive charge, which attracts more platelets which initially have a negative charge.
What do PLTs provide a surface for?
Formation and deposition of fibrin
How doe platelets help facilitate wound closure and vessel patency?
Clot reatraction via actinomyosin filaments
How do you determine PLT concentration in blood? (2 ways)
Blood smear
Hematology analyzers
How do you evaluate PLT morphology? (2 ways)
Blood smear
Hematology analyzers
How do you evaluate PLT function?
Bleeding time tests
How do you evaluate PLT production?
Bone marrow aspirate
How many PLTs should you have on a smear?
At least 7-10 PLTs/OIF (horses at least 4-7 PLTs/OIF)
What do you need to watch for when reading a smear for platelets?
Clumping, especially in cats and cattle
What ranges are given for mild, moderate and severe thrombocytopenia?
Mild = 80,000 - 150,000/uL Moderate = 30,000 - 80,000/uL Severe = <30,000/uL
What PLT number means spontaneous hemorrhage?
<20,000/uL
What is thrombocytosis?
PLT higher than reference interval
What species do you see more PLT size variation in?
Cats
What species has pale staining PLTs?
Horses
What does increased numbers of large PLTs suggest?
Active production of PLTs
What does increase MPV suggest with regards to platelets?
Thrombopoiesis
What is the purpose of a bleeding time test?
To test PLT function
What is the BMBT?
Buccal Mucosal Bleeding Time
What are normal BMBTs for dogs, cats and horses?
Dog = 1 - 5 min Cat = 1 - 3.5 min Horse = 8 - 10 min
How is the cuticle bleeding time test done?
Cut the apex of the quick with guillotine clippers and measure time for bleeding to stop.
What is the time for dogs to stop bleeding with the cuticle bleeding time test?
2-8 minutes
When would you do a bone marrow aspirate to look at platelets? (2 reasons)
When you see a pancytopenia
Low PLT numbers with no obvious reason.
What are 2 causes of low PLT numbers in the bone marrow?
Neoplasia
Crowding by other cells
T/F; Thrombocytopenia is a specific disease.
False. Thrombocytopenia is diagnostic problem
What are the 5 clinical features of thrombocytopenia?
Mucosal bleeding Petechiation Ecchymosis Spontaneous hemorrhage \+/- Hemorrhagic anemia
What are the 4 main mechanisms of thrombocytopenia?
Production
Consumption
Sequestration
Loss
T/F: Hemorrhage doesn’t cause thrombocytopenia, but thrombocytopenia can cause hemorrhage.
True
Exception is acute, severe hemorrhage may cause a mild thrombocytopenia.
What are 3 common causes of thrombocytopenia due to consumption?
DIC
Vasculitis (rickettsials, FIP)
Viral infection
What degree of thrombocytopenia do you see with consumption?
Mild to moderate
What is a major cause of thrombocytopenia due to destruction?
Immune mediated thrombocytopenia
What two species are susceptible to alloimmune thrombocytopenia?
Piglets
Foals
How can MLV vaccines result in thrombocytopenia?
Can induce immune response against the PLTs, which then aggregate and are cleared 3-10 days post-vaccination.
What degree of thrombocytopenia do you see in cases of PLT destruction?
Severe thrombocytopenia
What will you find in a CBC with thrombocytopenia due to destruction? (3 things)
Severe thrombocytopenia
+/- acute hemorrhagic anemia
+/- leukocytosis
NOTE: (PT and PTT will be normal)
What will you find in a bone marrow aspirate with thrombocytopenia due to destruction?
Increased megakaryocytes
What will the results of anti-platelet antibody tests be with thrombocytopenia due to destruction?
Positive
What will serum biochemistry be with thrombocytopenia due to destruction?
Normal
What are 3 causes of decreased PLT production?
Bone marrow hypoplasia
Neoplasia
Myelonecrosis or myelofibrosis
Where might PLTs get sequestered?
In large vascular beds
What are 4 cases of PLT sequestration/abnormal distribution?
Splenomegaly, torsion, neoplasia
Hepatomegaly, portal hypertension
Vasodilation in endotoxic shock
Severe hypothermia
When can you see a pseudothrombocytopenia? (2 things0
Analyzer can’t measure because PLTs are to obig, or clumped
What are the two major mechanisms in thrombocytosis?
Increased production
Increased distribution
Are animals symptomatic with increased platelet count?
No
What is the primary cause of thrombocytosis?
Neoplastic production of PLTs
What is the secondary cause of thrombocytosis? (2 things)
Reactive thrombocytosis associated with some diseases.
Associated with certain situations
What is a major cause of reactive thrombocytosis?
Chronic inflammatory disease
What do you suspect in an animal with clinical signs of thrombocytopenia, but a normal platelet count?
Qualitative disorders
What are 4 acquired causes of qualitative platelet disorders?
Uremia
Drugs
Fibrin degradation products (FDPs)
Paraproteins
What are 4 inherited causes of qualitative platelet disorders?
No glycoprotein receptors
No or reduced granules
Signal transduction defects
vWF deficiency***
What is the main result of vWF deficiency?
Decreased platelet adhesion
What are the two forms of vonWillebrand Disease?
Quantitative deficiency (Type 1, Type 3) Qualitative deficiency (Type 2)
What is the severity of Type 1 von Willebrand Disease?
Mild, dogs usually subclinical
What is the severity of Type 3 von Willebrand Disease?
Severe
What is the main clinical feature with vWD?
Mild to severe bleeding
How is vWD diagnosed? (5 things)
Based on signalment, history, medications, other primary disorders, Platelet/Coagulation evaluation
What 3 diseases can cause thrombocytosis?
Chronic inflammatory disease
Iron deficiency anemia
IMHA
What are 3 situations that can cause thrombocytosis?
Post-splenectomy
Excitement
Response to drugs (Vincristine)
Rebound from thrombocytopenia
What test can confirm vWD?
Run plasma vWD concentration