Platelets Flashcards
Platelets
Initial hemostatic plug
Temporary
Coagulation proteins
Reinforce the platelet framework and part of definitive hemostatic plug
What is the precursor cell to platelets
Megakaryocyte, cytoplasmic fragments
How are platelets released in blood
Megakaryocyte in bone marrow and reach out branches into the blood vessel and the sheer flow of blood will cause portions of the cytoplasm to break off
Platelet regulation
Thrombopoietin from the liver at a constant rate and removed from blood by circulating platelets. If platelet mass reduces there is an increase in TPO concentration resulting in increased production. Inflammatory cytokines also increase production
Thrombopathia
Qualitative disorder of platelets
Extrinsic platelet disorder
Platelets are normal but there is some other part of the way the platelets work is not. IE von Willebrand factor missing
Intrinsic platelet disorder
Platelets are abnormal
4 categories of platelet disorders
- Congenital for abnormal conc
- Acquired causes for abnormal conc, most common
- Congenital functional defect
- Acquired functional defect
Platelet type bleeding from thrombocytopenia or thrombopathia
Bleeding from mucosal surfaces including: epistaxis, gingival, UT, and GI bleeding. See petechial or ecchymotic hemorrhage on any skin or mucosal surface
At what point can you get spontaneous bleeding due to low platelet conc?
<50,000platelets/ul
Mean platelet volume
MPV from automated platelet concentration.
Average size of circulating platelets
High MPV with thrombocytopenia
Megakaryocytes are trying to respond to low platelet numbers. Not you and will stay that big. Good sign
Low MPV with thrombocytopenia
May indicate insufficient number of megakaryocyte present or failure to response
Normal MPV in thrombocytopenia
Megakaryocytes not responding or it is too early for response
When do we test platelet function
When the concentration is adequate but have platelet type bleed
Buccal mucosal bleeding time
Indicate primary hemostasis or platelet status. Only use on pt with adequate platelet concentrations. Can’t be used to detect coagulopathies
Clot retraction
Test platelet function and do not do on pt with medications that affect clotting. Tests to see if blood mixed with thrombin will form a clot retraction. Always do duplicates and with control
Platelet aggregometry
Gold standard. Highly specialized and not readily available and must be completed quickly
Cats and platelets
-Tend to be more clumped (reactive)
-Variable size
-See more giant platelets
-Do not use impedance hematology analyzers
-Often have no clinical signs of thrombocytopenia
Inherited macrothrombocytopenia signalment
Cavalier King Charles are poster child
Inherited macrothrombocytopenia
Low number but larger so there is no clinical bleeding
Immune mediated thrombocytopenia
Circulating platelets or megakaryocytes destroyed by immune mediated mechanism
Causes of ItP
- Primary or autoimmune
- Secondary to immune complex absorption or neoantigen expression
- Incompatible transfusion
Rickettsial induced thrombocytopenia
-Erlichia canis
-Anaplasma platys and phagocytum
-Rickettsia rickettsia
Have immune mediated clearance and decreased lifespan as well as vasculitis induced consumption
Drug induced thrombocytopenia
-Primary-> destroyed by drug interaction
-Secondary immune mediated-> drug dependent (if you stop drug and stops reaction to platelets) or independent
-Secondary bone marrow suppression
DIC
Pathologic process characterized by widespread activation of clotting cascade and get clots throughout body and use up all the platelets. See if there is massive tissue damage
Destruction or crowding of marrow cavity thrombocytopenia
Inflammatory disease
Myeloproliferative disease
Myelopthsis/myelofibrosis
Von Willebrand disease
Most common congenital extrinsic platelet function disorder in dogs. Decreased VW factor reduces platelet adhesion
Diagnosis of von Willebrand
ELISA to determine antigen levels using plasma not serum
Clot retraction and APTT is normal
Diagnosis of von Willebrand
ELISA to determine antigen levels using plasma not serum (EDTA or citrated plasma)
DNA test is available
Clot retraction and APTT is normal
Glanzmann Thrombasthenia
Congenital intrinsic platelet dysfunction. No clot retractions. Defect in GpIIb-IIIa so abnormal fibrinogen binding and unable to aggregate platelets
CalDAG-GEFI Thrombopathia
Congenital intrinsic platelet dysfunction. Abnormal signal transduction so decreased binding of platelets to fibrinogen. Normal clot retraction
Acquired Qualitative Platelet Function disorders
-FeLV
-Drug induced (TXA2)
