20 - Platelets Flashcards
circulating life span of platelet
7-10 d
what fraction of platelets are sequestered in spleen?
1/3
what does TPO bind to on megakaryocytes?
c-MPL
nl MPV
7-11 fL
GP2b-3a
fibrinogen receptor on platelets
undergoes conf change when platelet is activated to give it high affinity for fibrinogen
GP1b-IX-V
vWF receptor on platelets
alpha vs delta granules of platelets
alpha - more of them, vWF, platelet factor 4, fibrinogen, factor V
delta - ADP, ATP, serotonin, Ca, Mg
Bernard Soulier syndrome
abnormal GP1b-IX-V > giant platelets and thrombocytopenia
dec aggregation w/ ristocetin, nl to other agonists
storage pool diseases
alpha granule deficient - gray platelet syndrome
dense granule deficient - Hermansky Pudlak
causes of acquired platelet dysfunction
aspirin, NSAIDs other drugs - beta lactam abx (esp older cephalosporins), CCBs, SSRIs renal failure liver disease cardiopulm bypass myeloproliferative disorders dysproteinemias
main symptom of platelet disorders
mucocutaneous bleeding
at what platelet count does excessive surgical bleeding start to be seen or problematic?
<50k/ul
at what platelet count should you transfuse the pt?
<10k otherwise
at what platelet count is the pt at high risk for spontaneous bleeding?
<5k
3 main things that should be on the differential for thrombocytopenia
immune mediated (including drugs) thrombotic microangiopathy (TTP, HUS, HELLP) DIC
ITP pathophys
inc platelet destruction due to phagocytosis of ab coated platelets
autoantibodies (mostly IgG) cross react w/ nl platelet glycoproteins
causes of ITP
neoplasia (hodgkin’s, NHL, CLL, solid tumors)
autoimmune (SLE, APS, AIHA, thyrotoxicosis, primary ITP - in kids)
immune dysregulation (HIV, etc)
alloimmune (post transfusion purpura, neonatal alloimmune thrombocytopenia)
tx for ITP
steroids, IVIG, anti-D Ig
platelet transfusion NOT helpful usually
2nd line:
splenectomy, rituximab, addl immunosuppressors
a major cause of drug induced ITP
heparin induced thrombocytopenia (HIT)
classic pentad of TTP
fragmentation hemolysis thrombocytopenia fluctuating neuro changes renal insufficiency fever
diagnostic triad of TTP
fragmentation hemolysis
thrombocytopenia
elevated LDH
acute tx for TTP (dos and don’ts)
plasma exchange, steroids, plasma infusion
DONT: platelet transfusion, anti platelet drugs, DDAVP
4 kinds of inherited thrombocytopenia
May Hegglin
Bernard Soulier
Wiskott Aldrich
Fanconi Anemia
May-Hegglin
non muscle heavy chain of myosin mutation
Dohle like inclusions
giant platelets
thrombocytopenia
