Platelets

Question 1

lifespan and distribution of platelets

Answer 1

lifespan 9-10 days

distribution 1/3 in spleen, 2/3 in circulation

Question 2

conditions associated with macrothrombocytes

Answer 2

ITP
Bernard-Soulier
May-Hegglin
Montreal platelet syndrome
Gray platelet syndrome

Question 3

conditions associated with microthrombocytes

Answer 3

Wiskott-Aldrich
TAR
CMV infection

Question 4

most common antigen involved in NAIT?

Answer 4

HPA1a (75%), others: HPA-5b

Question 5

what is the risk of ICH in a baby with NAIT

Answer 5

10-20% - frequently occurs in utero

Question 6

what antibodies should you screen for in NAIT?

Answer 6

HPA1, 3, 5 (and 4 if asian)

Question 7

natural hx of NAIT?

Answer 7

recovery of platelet count by 2-3 weeks

Question 8

treatment of NAIT?

Answer 8

platelet transfusion (try random donor, unmatched platelets first - can try washed maternal platelets if ineffective)
IVIG 1g/kg/day x 1-3 days
methylpred
HUS
goal of tx: platelets > 30-50
if ICH: platelets > 100

Question 9

which usually causes the most severe thrombocytopenia, NAIT or neonatal autoimmune thrombocytopenia?

Answer 9

NAIT - usually < 50

with neonatal autoimmune thrombocytopenia, 10-15% have plts < 50 (including less risk of ICH)

Question 10

what is the antigen target of autoantibodies in neonatal autoimmune thrombocytopenia?

Answer 10

usually GPIIB/IIIA or GPIb/IX complexes

Question 11

duration of low platelets in neonatal autoimmune thrombocytopenia?

Answer 11

approx 3 weeks

Question 12

how common is thrombocytopenia in down syndrome

Answer 12

85% of neonates with T21 will have low platelets

Question 13

weak platelet activators

Answer 13

ADP

epinephrine

Question 14

potent platelet activators

Answer 14

collagen

thrombin

Question 15

role of glycoprotein GPIa/IIa integrin receptor on platelet cell surface?

Answer 15

to bind collagen, resulting in platelet activation

Question 16

what cell surface receptor changes conformation after platelet activation?

Answer 16

GPIIa/IIIb - resulting in binding to fibrinogen and vWF

Question 17

what receptor is mutated in Glanzmann’s thrombasthenia?

Answer 17

GPIIa/IIIb

Question 18

what is contained in platelet alpha granules?

Answer 18

fibrinogen, vWF, PDGF, p-selectin, thrombospondin, platelet factor 4

Question 19

what is contained in platelet dense granules?

Answer 19

ADP, ATP, ionized calcium, histamine, serotonin

Question 20

definition of chronic ITP

Answer 20

platelets < 100 lasting 12 months after presentation

Question 21

definition of refractory ITP

Answer 21

requires further tx after splenectomy

Question 22

what should you screen for before giving rituximab?

Answer 22

hepatitis B

risk of reactivation

Question 23

what are the TPO receptor agonists?

Answer 23

romiplostim and eltrombopag