20 - Platelets

Question 1

circulating life span of platelet

Answer 1

7-10 d

Question 2

what fraction of platelets are sequestered in spleen?

Answer 2

1/3

Question 3

what does TPO bind to on megakaryocytes?

Answer 3

c-MPL

Question 4

nl MPV

Answer 4

7-11 fL

Question 5

GP2b-3a

Answer 5

fibrinogen receptor on platelets

undergoes conf change when platelet is activated to give it high affinity for fibrinogen

Question 6

GP1b-IX-V

Answer 6

vWF receptor on platelets

Question 7

alpha vs delta granules of platelets

Answer 7

alpha - more of them, vWF, platelet factor 4, fibrinogen, factor V
delta - ADP, ATP, serotonin, Ca, Mg

Question 8

Bernard Soulier syndrome

Answer 8

abnormal GP1b-IX-V > giant platelets and thrombocytopenia

dec aggregation w/ ristocetin, nl to other agonists

Question 9

storage pool diseases

Answer 9

alpha granule deficient - gray platelet syndrome

dense granule deficient - Hermansky Pudlak

Question 10

causes of acquired platelet dysfunction

Answer 10

aspirin, NSAIDs
other drugs - beta lactam abx (esp older cephalosporins), CCBs, SSRIs
renal failure
liver disease
cardiopulm bypass
myeloproliferative disorders
dysproteinemias

Question 11

main symptom of platelet disorders

Answer 11

mucocutaneous bleeding

Question 12

at what platelet count does excessive surgical bleeding start to be seen or problematic?

Answer 12

<50k/ul

Question 13

at what platelet count should you transfuse the pt?

Answer 13

<10k otherwise

Question 14

at what platelet count is the pt at high risk for spontaneous bleeding?

Answer 14

<5k

Question 15

3 main things that should be on the differential for thrombocytopenia

Answer 15

immune mediated (including drugs)
thrombotic microangiopathy (TTP, HUS, HELLP)
DIC

Question 16

ITP pathophys

Answer 16

inc platelet destruction due to phagocytosis of ab coated platelets
autoantibodies (mostly IgG) cross react w/ nl platelet glycoproteins

Question 17

causes of ITP

Answer 17

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)

Question 18

tx for ITP

Answer 18

steroids, IVIG, anti-D Ig
platelet transfusion NOT helpful usually

2nd line:
splenectomy, rituximab, addl immunosuppressors

Question 19

a major cause of drug induced ITP

Answer 19

heparin induced thrombocytopenia (HIT)

Question 20

classic pentad of TTP

Answer 20

fragmentation hemolysis
thrombocytopenia
fluctuating neuro changes
renal insufficiency
fever

Question 21

diagnostic triad of TTP

Answer 21

fragmentation hemolysis
thrombocytopenia
elevated LDH

Question 22

acute tx for TTP (dos and don’ts)

Answer 22

plasma exchange, steroids, plasma infusion

DONT: platelet transfusion, anti platelet drugs, DDAVP

Question 23

4 kinds of inherited thrombocytopenia

Answer 23

May Hegglin
Bernard Soulier
Wiskott Aldrich
Fanconi Anemia

Question 24

May-Hegglin

Answer 24

non muscle heavy chain of myosin mutation
Dohle like inclusions
giant platelets
thrombocytopenia