Platelets Flashcards
(50 cards)
How are platelets formed?
- liver makes thrombopoietin
- megakaryocytes get bigger b/c of its dividing DNA and the cytoplasm stretches
- platelets are shed from disintegrating megakaryocyte
What do phospholipids and glycoprotein receptors on the platelet cell membrane do?
- phospholipids important in coagulation and fibrin clot formation
- glycoprotein receptors needed for platelet adhesion and aggregation
What do dense granules in platelets do?
-contribute to platelet aggregation and anticoagulation activity
What do alpha granules do in platelets?
-contain proteins that contribute to adhesion, aggregation and coagulant activity
What does a high platelet volume suggest?
-young platelets and a destructive process
What does a low platelet volume suggest?
-older platelets and a marrow production issue
Platelet Function Assay
-in vitro test of platelet function that has replaced bleeding time test
-esp useful in von Willebrand’s disorder
-if collagen/epinephrine and collagen/ADP are both long, platelet dysfunction
(if epi only, ASA or drug effect)
Myeloproliferative Disorders
- abnormal platelets and too many platelets
- thrombosis is a big worry
- treat dz, give ASA or other antiplatelet med
Examples of Myeloproliferative Disorders
- essential thrombocytopenia
- chronic myelogenous leukemia
- polycythemia vera
Reactive Platelet Disorders
- normal platelets but too many
- will resolve with time
Causes of Reactive Platelet Disorders
- infection
- post-splenectomy
- malignancy
- iron deficiency
- inflammation
What are 3 mechanisms that can cause thrombocytopenia (too low platelets)?
- decreased production
- increased destruction
- hypersplenism
What might cause decreased platelet production?
- bone marrow failure (aplastic anemia)
- marrow replacement (lymphoma, leukemia)
- marrow toxins (drugs, radiation, ethanol)
- nutritional deficiency (B12, folic acid)
What might cause drug-induced thrombocytopenia?
- myelosuppression: chemo, sulfa drugs, VPA, anti-retrovirals
- immunologic: drug might induce antibody response
Clinical/Lab Presentation of Drug-Induced Thrombocytopenia
-severe, rapid onset of thrombocytopenia
Treatment of Drug-Induced Thrombocytopenia
- stop drugs
- transfuse platelets if necessary
Clinical Features of Heparin-Induced Thrombocytopenia
- thrombocytopenia starts 5-10 days after starting heparin
- absence of other causes of thrombocytopenia
- return to normal platelet count when heparin is discontinued
Lab Features of HIT
- low platelets
- variable INR, PTT, fibrinogen
What is concerning about HIT?
How is HIT treated?
-can cause life or limb-threatening venous and/or arterial thrombosis
- stop all forms of heparin ASAP
- alternative anticoagulants (fondaparinux, argatroban, etc)
What is immune thrombocytopenic purpura?
loss of tolerance to self and IgG antibody against platelet glycoproteins
Immune Thrombocytopenia Purpura in Kids
- acute onset often after viral illness
- often resolves spontaneously
Immune Thrombocytopenia Purpura in Adults
- insidious onset
- many pts go on to have chronic ITP
Clinical Features of ITP
- most kids have no health issues
- most adults have other issues like autoimmune or malignancy
- petechiae in dependent regions, ecchymoses
- menorrhagia, epistaxis, gingival bleeding, blood in stool or urine
- no lymphadenopathy or splenomegaly
Lab Features of ITP
- very low platelets (< 10,000)
- CBC otherwise normal
- normal coagulation times (INR, PTT, fibrinogen)
