Platelets Flashcards
Decreased platelets or loss of function, decreased coagulation factors or loss of function, or increased fibrinolysis can cause what kind of hemostasis imbalance?
Hemorrhage
*Immune-med thrombocytopenia
Increased procoagulation activity or decreased fibrinolysis can cause what kind of hemostasis imbalance?
Excessive thrombus formation (leads to obstructed blood flow and local hypoxia)
*Protein-losing nephropathy
What part of the platelet can evert into pseudopodia to trap microorganisms and viruses?
Canalicular and tubular systems
What are the 2 types of granules platelets have?
Alpha and dense
Large cells located at the bone marrow sinus, with long propatelet processes that extend into the sinus lumen, that have a polyploid nucleus with 8-64 copies of the genome.
Megakaryocytes
How long does it take to go from megakaryoblast > megakaryocyte > platelet release?
4-5 days
This glycoprotein hormone is produced by the liver, binds to receptors on platelets, and induces megakaryocyte production and differentiation.
Thrombopoietin
What happens with thrombopoietin when there is a decrease in the number of platelets?
A decrease in PLT number leads to increased free plasma TPO, which then stimulates the bone marrow to make more platelets.
When stimulated, how does the bone marrow increase PLT production?
Increased number, size, and ploidy of megakaryocytes
Decreased megakaryocyte maturation time
Primary hemostasis, or the formation of a primary hemostatic plug, takes 3-5 minutes. What are the steps?
PLTs adhere to subendothelium
PLTs undergo activation
Aggregation to form platelet plug
GB1b on the PLT surface has to bind to what factor in the subendothelium in order to adhere?
von Willebrand Factor (vWF)
When PLTs are activated, they undergo a shape change from smooth discs to spheres with filopodia by flipping their membranes. What is this a response to?
Thrombin
What happens during PLT activation?
Shape change
Membrane flip: phosphatidylserine to the outside (neg)
Secretion of granule products
Why would a hypocalcemic patient be more at risk of hemorrhage?
Calcium is required for platelet aggregation and plug formation
Formation and deposition of fibrin occurs during ______ hemostasis.
secondary
Clots contract via _____ _______ to facilitate wound closure and vessel patency.
actin myofilaments
What tests would you do to determine PLT morphology and concentration?
Blood smear
Hematology analyzer
What tests would you do to determine PLT functionality?
Bleeding time tests
PLT function tests
What would you look at to determine if PLT production is normal?
Bone marrow aspirate
Why should blood be collected in EDTA tubes for PLT counts?
Chelates Ca++ and prevents clotting so individual platelets can be counted
What is the minimum amount of PLTs you should see per 100x field? What about in a horse?
7-10
Horse: 4-7
What species has more size variation in PLTs, and a tendency for PLT clumps?
Cats
A blood smear shows increased numbers of PLTs the same size or larger than the RBCs. What does this indicate?
Macroplatelets indicate active platelet production
Although an analyzer will give a more accurate platelet count that a blood smear, why is it still important to look at the smear?
PLT clumps will give falsely low PLT numbers
Normal PLT counts are about 200,000/uL. What are the numbers for mild, moderate, and severe thrombocytopenia?
Mild: < 80,000/uL
Moderate: 30,000 - 80,000/uL
Severe: < 30,000/uL (risk for spontaneous hemorrhage)
What can we diagnose from a thrombocytosis?
Supportive evidence of other disease processes (ie: Fe++ deficiency anemia)
The buccal mucosal bleeding time (BMBT) tests platelet function. When prolonged, it can indicate what problems with the PLTs?
Decreased PLT function
Decreased PLT numbers (more common - do PLT count before this test)
What are the reference intervals for the BMBT in cats, dogs, and horses?
cats: 1-3 mins
dogs: 2-4 mins
horses/cattle: 8-10 mins
T/F: The BMBT is highly sensitive and specific, and a normal clotting time indicates normal PLT function and number.
FALSE
Not sensitive or specific. Can be normal and there can still be a problem. But, if abNL, something is wrong.
Mucosal bleeding, petechiation, ecchymosis, spontaneous hemorrhage, and hemorrhagic anemia are possible clinical signs associated with:
Thrombocytopenia
WHAT ARE THE MECHANISMS OF THROMBOCYTOPENIA?
Decreased production
Destruction
Sequestration
Loss
Consumption
*pseudothrombocytopenia (clumping and macroplatelets)
What diseases can cause a thrombocytopenia due to decreased production?
Bone marrow hypoplasia
Neoplasia (leukemia or metastatic)
Myelobecrosis/Myelofibrosis
What mechanism of thrombocytopenia tends to be severe and can lead to spontaneous hemorrhage?
Destruction
Alloimmune thrombocytopenia in piglets, in which the offspring ingests anti-platelet Ab in the colostrum, and dies from hemorrhage, is what mechanism of thrombocytopenia?
Destruction
A client wants to have his puppy spayed just a few days after finishing a series of modified live vaccines. You suggest waiting at least 2 weeks. Why?
Modified live virus vaccines may induce an immune response against PLTs and cause a mild thrombocytopenia that can last about 2 weeks.
You’re examining a new foal who has some blood in its urine. You notice bleeding from mucosal membranes and petechiae. You do a CBC and note severe thrombocytopenia, but the PT and PTT are normal. A bone marrow aspirate shows increased megakaryocytes. What do you suspect is wrong with this foal?
Immune-mediated thrombocytopenia
You do xrays on a horse with moderate thrombocytopenia and discover nephrosplenic entrapment. How can this contribute to low PLT numbers?
Sequestration of PLTs in the spleen due to torsion
What diseases can cause thrombocytopenia via consumption?
DIC, FIP, rickettsial disease
T/F: Like in humans, thrombocytosis in animals is associated with risk for hemorrhage and thrombosis.
FALSE
Animals are generally asymptomatic. It is often an incidental finding.
Why might a dog with Fe++ deficiency anemia have a thrombocytosis?
Reactive to the underlying disease
What are the 2 types of primary thrombocytosis?
Essential thrombocythemia (myeloproliferative disease)
Megakaryoblastic leukemia (RARE)
Why does inflammation cause reactive thrombocytosis?
IL-6 increased TPO production
*Immune-mediated diseases!
What endocrine disease can cause a reactive thrombocytosis?
Cushing’s Syndrome
*and administration of glucocorticoids
Acute massive PLT losses from splenectomy, managed ITP, and Ehrlichia, can cause _______ thrombocytosis.
Rebound
Splenic contraction in excited horses and the chemotherapeutic Vincristine can cause secondary _______.
thrombocytosis
What are examples of acquired qualitative platelet disorders?
Uremia
Drugs (aspirin, acetaminophen, phenylbutazone, NSAIDS, anesthetics)
Fibrin degradation products (FDPs inhibit PLT function)
Paraproteins (plasma cell myeloma)
What are the inherited issues with PLT quality?
Von Willebrand’s Disease!
Absence of glycoprotein receptors
Absence/reduction in granules
Signal transduction defects
A 1 year old Doberman Pinscher presents to the ER post-op with severe bleeding. PLT counts are normal, and PTT/ACT are normal. BMBT is prolonged. Based on the test results and signalment, what form of vWD do you suspect this dog has?
Type 3 - quantitative
*more severe, and may indicate deficiency of Factor VIII if PTT/ACT is prolonged
A German Shepherd presents for vWD testing before elective surgery. The dog isn’t showing any signs and PLT counts are normal. What test should you run to determine if the dog has the subclinical form of the disease?
vWF Antigen Concentration
The German Shepherd that was in for vWD testing has a vWF protein concentration of 49%. Does this dog have vWD?
YES! Normal result on the vWF Ag Concentration test should be 100%. Anything under 50% is a deficiency.
Routine labs are performed on a Cavalier King Charles Spaniel and the PLT count is decreased, while the PLT MCV is increased. The dog is not showing any signs. What is causing macrothrombocytopenia in this dog?
Congenital macrothrombocytopenia
*B1-tubulin gene mutation that causes macrothrombocytes
