Hematology - Hemostasis 1 Flashcards
What are the stages of hemostasis?
Primary, secondary, and tertiary hemostasis
What occurs during primary hemostasis?
The formation of the platelet plug
What is primary hemostasis sufficient for?
small vessel injury
What occurs during secondary hemostasis?
The formation of the fibrin clot through the coagulation cascade
What is secondary hemostasis needed for?
medium/large vessel injury
What occurs during tertiary hemostasis?
Fibrinolysis to re-establish blood flow through vessels
What clinical signs are associated with primary hemostatic defects?
Mucosal surface bleeding: petechiae, ecchymoses, epistaxis, hemoptysis, hematuria, hematemesis, melena, hematochezia, ocular bleeding, and CNS bleeding
What are the key cellular players in primary hemostasis?
endothelial cells and platelets
What are the key protein adhesive agents in primary hemostasis?
Von Willebrand factor (vWF), collagen, and fibrinogen
What are the key protein agonist agents in primary hemostasis?
ADP, thromboxane A2 (TXA2), and thrombin
What prevents platelet adhesion in the normal vessel?
Negatively charged endothelium, NO, prostacyclin, and ADPase
When subendothelium is exposed, what occurs during primary hemostasis?
von Willebrand facort binds to the subendothelium, a platelet enzyme binds to the subendothelial vWF, and the aggregation receptor becomes activated. Then another receptor binds to fibrinogen and in simple terms, more platelets are recruited and aggregate.
How do activated platelets set stage for secondary hemostasis?
Activated platelets flip their membranes which exposes phosphatidylserine and then provide a docking site for clotting factors needed in secondary hemostasis
Generally, what can go wrong with primary hemostasis?
Low platelet number, impaired platelet function, deficient vWF number, impaired vWF function
What is the most common acquired disorder of primary hemostasis?
thrombocytopenia
What can cause thrombocytopenia?
Use, destruction, and decreased production
What inherited disorder can lead to thrombocytopenia?
Congenital macrothrombocytopenia
What breeds is congenital macrothrombocytopenia common in?
Cavalier King Charles Spaniels, Norfold Terriers, and others
What occurs in congenital macrothrombocytopenia?
The patients don’t bleed because their platelets are too big
What are common acuired causes of thrombocytopenia?
Immune-mediated, infectious disease, DIC, and drugs
What is thrombopathia?
platelet dysfunction
What are the forms of thrombopathia?
inherited and acquired
What are the acquired causes of thrombopathia?
DIC, renal and liver disease, and drugs
What is the most common inherited primary hemostatic disorder?
von Willebrand’s disease
What breeds is vWD most common in?
Dobermans, German shorthaired pointers, scottish terriers, and many others
If you suspect a hemostatic defect, what testing should be done?
Platelet count and coagulation profile
How do you estimate the platelet count from a blood smear?
count in a 100x field - 1 per field equals 20,000 platelets/ul
At what platelet count will spontaneous bleeding occur?
Less than 30,000
How do you do vWD testing?
With vWF:Ag testing
When should you perform vWD testing?
If the patient is of a predisposed breed, young, and previous bleeding
How do you test platelet function?
Buccal mucosal bleeding time, platelet function analyzer, and specific platelet function tests
What will cause BMBT to be abnormal (greater than 4 minutes)?
Thrombocytopenia, thrombopathic, vWF deficient/abnormal, and abnormal vasculature
When should you do BMBT?
When other screening tests are normal - clotting times, platelet count, and >30% vWF:Ag
Why is a platelet function analyzer not the best option?
Not all laboratories have them and they are not specific for which platelet defect
What do specific platelet function tests require?
Specialized equipment and fresh platelets (in reference to their patient, not their blood)
What are the generalized causes of thrombocytopenia?
Consumption of platelets, destruciton, decreased production, and sequestration
When does appropriate consumption of platelets occur?
bleeding
When does inappropriate consumption of platelets occur?
DIC
True or false: Immune thrombocytopenia is a disorder that is of people and dogs. It is rare in cats.
TRUE
What are the secondary causes of immune thrombocytopenia?
Drugs, infectious agents, and neoplasia
What testing should be done to rule out secondary causes of ITP?
Tick panel, imaging, thorough drug history
How is immune thrombocytopenia treated?
Immunosuppression just like for IMHA, glucocorticoids +/- a second agent
What emergency measures can be taken to treat immune thrombocytopenia?
Vincristine and IVIG
How does vincristine work?
It prevents microtubule polymerization and accelerated megakaryocyte fragmentation and platelet release from bone marrow
Can vincristien be used to treat IMHA?
NO
What does IVIG stand for?
Intravenous human immunoglobulin
What does IVIG do?
It blocks mononuclear phagocyte Fc receptor so that macrophages cannot engulf Ab coated platelets and it reduces B cell antibody production
What platelet transfusion products are preferred in primary hemostasis patients?
Fresh whole blood, platelet rich plasma, platelet rich concentrate, cryoplatelets, and lyophilized platelets
What are cryoplatelets?
Platelet concentrate cryopreserved in DMSO
What are the indications for platelet transfusions?
Severe thrombocytopenia, suspect pulmonary or CNS hemorrhage, and acquired or hereditary thromnopathias
True or False: Plasma does not contain platelets.
TRUE
What is the prognosis for immune thrombocytopenia?
Good - only a 10-30% mortality rare
What are the natural inhibitors of primary hemostasis?
Endothelial cells as a physical barrier, ADPase, prostacyclin, and nitric oxide
What are the pathological inhibitors of primary hemostasis?
Disease - DIC, metabolites in liver and kidney disease, and paraproteins
What are the therapeutic inhibitors of primary hemostasis?
Platelet inhibitors - Aspirin, NSAIDS, and Clopidogrel
What does Aspirin and NSAIDs do to inhibit platelets?
They are Cox inhibitors and TxA2 production inhibitors that don’t allow platelets to activate their neighbors
How does Clopidogrel inhibit platelets?
It binds to their ADP receptor so that they cannot be activated
