17 - Laboratory Evaluation of Hemostasis 1 Flashcards
what are the steps of hemostasis
1- vascular spasm
2- platelet plug formation
3- blood clotting
vascular injury?
what is the life span of platelets in mammals
4-6 days
what is platelet senescence
increased membrane phosphatidylserine (PS)
how are aged platelets removed
by macrophages
where are some platelets stored
splenic storage
what do platelets do
- hemostasis
- vascular integrity
- various roles in inflammation and tumor metastasis
how do platelets cause hemostasis
platelet plug formation and they accelerate coagulation
** platelet procoagulant activity (prev. called platelet factor 3 PF3)
** platelet factor 4 - binds heparin and inhibits antithrombin activity
how do platelets adhere to the extracellular matrix
there is a GPlb/IX/V is a glycoprotein adhesion molecule complex on the platelet
—-> that binds to von Willebrand factor on the extracellular matrix
what shape change happens in platelets
unactivated platelets are round in shape and activated platelets develop filapodia
activation of platelet fibrinogen receptors
photo
activated platelets promote coagulation in vivo
what are 3 important hemostatic screening tests
- platelet counts
- mean platelet volume
- buccal bleeding time
what can platelet clumps cause during a platelet count
a false thrombocytopenia
– caused by platelet activation during blood collection and handling (esp. cats)
– EDTA anticoag ( Esp. horses)
how can you rule out false thrombocytopenia
verify by stained blood film examination
– automated platelet counts often unreliable in cats
what dog breeds tend to have lower platelet counts
- greyhounds
- polish ogar dogs
- cavalier king charles spaniels
what does an increased MPV mean in response to thrombocytopenia
enhanced thrombopoiesis
what can cause spuriously increased MPV
- platelet aggregates
- storage of blood at 5C
what is the main problem with MPV determinations
inaccurate when platelet activation and aggregation is present
Other problems
- MVP may not be reported when thrombocytopenia is severe or histogram shape is abnormal
- anticoagulant used and storage conditions may result in changes of MPV
what is buccal bleeding time used for
- primarily used as a platelet function test
generally <4 min in dogs and <3 mins in cats (less reliable in horses)
what can cause a false positive antiplatelets antibody test
- increased surface Ab following storage
- immune complexes may be absorbed to platelets
how does antiplatelet antibody assays work
flow cytometry that detect the natural antibodies (Ab) in the platelets surface
what is the problem with buccal bleeding time
- no value of significant thrombocytopenia is present
- imprecise with repeat bleeding times varying by as much as 2 mins
what is different about cat platelets
- larger with higher mean platelet volume (MPV)
- especially sensitive to activation during blood sample collection
platelet morphology
photo
macroplatelets
what is the first thing you do when you get a marked thrombocytopenia on blood work
examine a blood film
when does spontaneous hemorrhage from thrombocytopenia alone generally occur
does not occur unless platelet counts are below 25,000/uL
what should you consider if spontaneous bleeding occurs with platelet counts above 25,000/uL
DIC
what is the pathogenesis of thrombocytopenia
- decreased platelet production
- increased platelet utilization
- increased platelet destruction
- sequestration of platelets (spleen)
- massive hemorrhage
- inherited macrothrombocytopenias in dogs
list causes of decreased platelet production
- myelophthisis
- myeloid neoplasms
- aplastic anemia
- chronic Ehrlichiosis infection
- a megakaryocytic thrombocytopenia
- inherited cyclic hematopoiesis
what are the biggest causes of increased platelet utilization
DIC and thrombosis ***
what are some other reasons that platelet utilization can be increased
- vasculitis, hemangiosarcoma in dogs, and other disorders resulting in vessel injury
- platelet aggregation can be induced by inflammatory cytokines such as platelet activating factor (PAF)
- some snake venoms induce platelet activation and aggregation
list what can cause increased platelet destruction
- primary immune-mediated (autoimmune) thrombocytopenia, most common in dogs
- infectious agents (bacterial, viral, protozoal, fungal) may induce vascular injury, immune-complex absorption, and direct platelet effects
*** Tick-borne diseases including babesia, ehrlichia, anaplasma, cytauxzoon - secondary immune-mediated thrombocytopenia’s (drugs, infectious agents, neoplasia, SLE)
- neonatal alloimmune thrombocytopenia (rare in pigs, horses and mules)
- intravenous heparin (mild in horses)
- activation of macrophages (GM-CSF, M-CSF)
when are platelets sequestered
splenomegaly and hypothermia
what is it called when splenomegaly results in permanent removal of platelets
hypersplenism
platelet counts seldom decrease below —— due to hemorrhage alone
100,000/uL
- counts as low as 60,000/uL have been recorded in dogs with massive hemorrhage secondary to anticoagulant rodenticide poisoning
what is more likely present if an animal is transfused with stored blood following hemorrhage
thrombocytopenia
what are some breeds of dogs that are prone to hereditary macrothrombocytopenias
- cavalier king Charles spaniels (common defect)
- Norfolk and cairn terriers
- American akita dogs
also may-hegglin anomaly in pugs (also has neutrophil inclusions)
^^^^ no bleeding problems in above disorders (platelets mass in blood is normal)
bernard-soulier syndrome in cocker spaniels have mucosal bleeding
what are some clinical signs of platelet function defects
- unexplained superficial bruising of skin
- tendency for mucosal surface bleeding
- prolonged post-traumatic hemorrhage
what is seen in lab findings with platelet function defects
** prolonged bleeding time
- normal platelet counts, usually
- normal platelet morphology, usually
- normal coagulation test
acquired platelet function defects
hereditary platelet function defects
what is bernard-Soulier syndrome
an inherited platelet adhesion defect – defect in GPIX (GP9) gene
- in cocker spaniel dogs
- macrothrombocytopenia (increased MPV)
- mucosal bleeding disorders (epistaxis, hematuria, gingiva, vulva after mating)
- prolonger buccal mucosal bleeding time
what is glanzmann’s thrombasthenia
a GPIIb/IIIa deficiency in otterhounds and great pyrenees
what are the 2 signaling pathway defects in GPIIb/IIIa activation and what breeds of dog do they affect
CalDAG-GEFI defect in basset hound, eskimo spitz, landseer dogs
kindlin-3 deficiency in german shepherds
what are dense granule deficiencies
inherited platelet aggregation defects
- american cocker spaniels (ADP deficiency)
- chediak-higashi syndrome in cats (complete lack of dense granules)
what breed of dog is prone to ADP receptor P2Y12 defect (inherited platelet aggregation defect)
greater swiss mountian dog
are the signs of platelet procoagulant activity (PF3) defect in german shepherds
epistaxis, prolonged bleeding with cutaneous bruising after surgery, hyphema, intramuscular hematomas
what do you see on blood test with platelet procoagulant activity (PF3) defect
standard platelet function tests (mucosal bleeding time, clot retraction, and platelet aggregation and secretion) and coagulation tests (PT, APTT, ACT) are normal
what is platelet procoagulant activity (PF3) defect in german sheps
A defect in translocation and exposure of phosphatidylserine on the platelet surface, resulting in impaired coagulation in vivo
what is enhance platelet functions
activated or hyperactive platelets
list some reasons for enhanced platelet functions
- diabetes mellitus
- nephrotic syndrome
- EPO treatment
- FIP virus
- heartworm DZ
- allergic respiratory disease
what is von Willebrand disease (vWD)
a quantitative and sometimes qualitative defects in plasma vWF
a defect in platelet adhesion resulting in prolonged bleeding times
common in dogs
what breed is most frequently affected with vWD
Doberman pinschers
list some reasons for thrombocytosis
- some chronic inflammatory conditions
——– increased production of thrombopoietin (TPO) by inflammatory cytokines, especially IL-6 - ongoing hemorrhage, especially if iron deficiency is present
- some hemolytic anemias
- rebound response to thrombocytopenia
- within one week following splenectomy
- primary thrombocytosis is a myeloproliferative neoplasm (MPN) called thrombocythemia
primary thrombocytosis is a myeloproliferative neoplasm (MPN) called what
thrombocythemia
