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40 Cards in this Set
- Front
- Back
What is the hormonal stimulus for platelet synthesis?
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thrombopoietin
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What are the 3 coordinated steps of forming a platelet plug?
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Adhesion via vWF and endothelial injury; aggregation via fibrinogen binding to GP IIb/IIIa on platelets, and TxA2, ADP, and others; Platelet secretion of ADP, vWF, and factor V
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Early in coagulation, what serves as a phospholipid scaffold?
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Platelets
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What does abnormal platelet activation lead to?
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arterial occlusion, heart attacks, and strokes
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If you suspect thrombocytopenia, what is the first thing to do?
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rule out pseudothrombocytopenia
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At what level do symptoms of thrombocytopenia show? When does it become dangerous?
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Symptoms between 50,000-20,000. Life-threatening 20,000-10,000.
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What are the symptoms of thrombocytopenia?
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mucocutaneous bleeding, aka "oozing and bruising."
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What are the 3 general etiologies of thrombocytopenia?
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underproduction, splenic sequestration, and peripheral destruction.
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What is the hallmark of underproduction of platelets?
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Inadequate numbers of megakaryocytes in the bone marrow.
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What are two important drugs that can cause underproduction of platelets?
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chemotherapy and alcohol.
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What are the 2 classes of thrombocytopenia due to destruction?
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Non-immune mechanisms and immune mechanisms
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What are the 2 important types of non-immune peripheral destruction of platelets?
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DIC, and TTP
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Definition of DIC
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abnormal activation of coagulation, generation of thrombin, consumption of clotting factors, and peripheral destruction of platelets.
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What are the 4 most important diagnostic signs of DIC?
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Elevated PT (prothrombin time), elevated D-dimers or FDPs, low platelets, and maybe schistocytes if there is MAHA.
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Definition of TTP
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abnormal activation of platelets and endothelial cells, deposition of fibrin in the microvasculature, and peripheral destruction of red cells and platelets.
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What is the pentad of TTP symptoms and which are required?
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1. microangiopathic hemolytic anemia- characterized by high LDH and schistocytes. Required!
2. Thrombocytopenia, required! 3. fever: not always seen 4. renal manifestations: not always seen 5. neurologic manifestations: not always seen. |
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What clinical lab findings distinguish TTP from DIC?
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For thrombotic thrombocytopenia fibrinogen, PT, FDPs, D-dimers are all generally normal.
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What is generally thought to be the etiology of TTP?
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Antibodies attack ADAMTS-13, an enzyme that cleaves the multimers of vWF. Ultra-high weight multimers of vWF accumulate and lead to abnormal platelet adhesion and activation.
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Under what 4 condition is the risk of TTP increased?
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pregnancy, HIV/AIDS, bone marrow transplants, solid organ transplants.
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What is the most important treatment for TTP?
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plasma exchange removes some of the high-weight vWF and the auto-antibodies, and replace them with fresh ADAMTS-13
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what should you ABSOLUTELY not do for a patient with TTP?
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NO platelet transfusions. It will just "fuel the fire!"
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What can TTP overlap with?
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HUS, which is usually caused by intestinal infections like O157:H7
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What causes immune-mediated thrombocytopenia?
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antibodies binding to platelets, which are destroyed by macrophages.
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what is the diagnostic test for immune thrombocytopenia?
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none
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which drugs can cause immune thrombocytopenia?
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beta-lactams, sulfa drugs (especially bactrim), heparin, and quinine/quinidine
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Is ITP associated with splenomegaly?
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no
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What is ITP usually associated with in children?
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viral infections
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what is initial therapy for ITP?
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corticosteroids, then splenectomy if they don't work
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What are two adjunctive therapies for ITP?
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IVIG (IV Immunoglobulin), or Rho gam.
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What is the pathogenesis of thrombocytopenia due to splenic sequestration?
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splenomegaly
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What is the most common cause of splenomegaly?
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portal hypertension
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What are the two situations to use platelet transfusion in cases of thrombocytopenia or thrombocytopathy?
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treatment of bleeding, prophylaxis against bleeding.
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When may platelets be transfused for ITP?
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in cases of severe bleeding.
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When to transfuse for TTP?
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NEVER
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Will platelet transfusions work for thrombocytopenias due to splenic sequestration?
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no
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What are the two primary thrombocytoses to know?
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Essential thrombocythemia and polycythemia vera.
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What are the secondary thrombocytosis causes?
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inflammation, bleeding, iron deficiency
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How do you diagnose qualitative disorders of platelets?
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abnormal bleeding times.
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How does clopidogrel work?
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It blocks the action of ADP (a platelet agonist).
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What is Abcximab?
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Blocks GP IIb/IIIa
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