Platelets

Question 1

How much of our platelets are pooled in our spleens?

Answer 1

about 33%

Question 2

What are the four major platelet tests?

Answer 2

count
bleeding time (or new alt)
blood smear morphology
platelet aggregometry

Question 3

What are the four GENERAL causes fo thrombocytpenia?

Answer 3

artifactual
decreased production
increased destruction
increased sequestration

Question 4

What are the two GENERAL causes of thrombocytosis?

Answer 4

primary (neoplastic)

secondary

Question 5

What are some of the reasons you get artifactual thrombocytopenia?

Answer 5

EDTA-induced platelet clumping from the test tube

clotted specimen

platelet clumping in myelodysplastic or myeloproliferative disorders

Question 6

How can you tell if the thrombocytopenia is artifactual/

Answer 6

the lab’s supposed to figure it out

check the perpheral blood morphology

check a citrated blood (light blue top tube) PLT count

Question 7

What are some general causes of decreased PLT production?

Answer 7

decreased numbers of megakaryocytes due to aplastic anemia, viral infection or drug-induced suppression

or impaired productoin of platelets by megakaryocytes due to a myelodysplastic process or megaloblastic process

Question 8

What are some classic drugs that suppress megaK production?

Answer 8

chemo agents
thiazides
lasix
alpha interferon
quinine
sulfonamides
cimetidine/ranitidine
vancomycin

ETHANOL

Question 9

WHat are some immune causes of increased platelet destruction?

Answer 9

ITP
neonatal purpura
post-transfusion purpura
drug-induced immune thombocytopenia
HIT
autoimmune disorders

Question 10

What are some non-immune causes of platelet destruction?

Answer 10

increased loss (using them all up)

increased use due to pathologic clotting (DIC)

sequestration (hypersplenism)

Question 11

What causes immune thrombocytopenic purpura (ITP)?

Answer 11

presumed due to anti-platelet antibodies

associated with viral infections and autoI disorders

Question 12

If you suspect ITP and you want to treat it as such (with steroids or rhogam or rituximab), what do you get first?

Answer 12

the bone marrow biopsy

because all the drugs could affect the bone marrow. obviously get a smear before that

Question 13

What is the most common cause of severe neonatal thrombocytopenia?

Answer 13

fetomaternal platelet incompatibility

Question 14

What type of antibody accoutn for 90% of the cases of neonatal purpura in caucasians?

Answer 14

human platelet antigen 1a antibodies

if mom is HPA1a negative, and the baby daddy is likely positive (because negative is rare), then mom will make antibodies against baby’s platelets to cause a severe thrombocytopenia

Question 15

How do you make the diagnosis of neonatal purpura in caucasians?

Answer 15

mom’s serology

mom and dad’s platelet antigen testing

genotype parents and baby

Question 16

How do you treat neonatal purpura?

Answer 16

Prenatal IVIg/G or transfuse infant with ABO compatible/HPA-1a negative platelets

Question 17

Who gets post-transfusion purpura?

Answer 17

HPA-1a negative individuals

Question 18

What is the factor will some Heparin bind that will lead to HIT?

Answer 18

platelet factor 4, which the platelet IgG will bind to and then you get the complexes that the body forms antibodies against

Question 19

Which type of hepatin has the higher incidence of HIT?

Answer 19

bovine is a higher molecular weight, so seems to bind up more PF4

Question 20

What percentage of patients who receive unfractionated (mixed) heparin will develop HIT?

Answer 20

2-20%

Question 21

How do we diagnose HIT now?

Answer 21

ELISA for Heparin-PF4 complex

(has replaced the hep-associated PLT aggregation test because it does NOT require a heparin-free specimen)

can also do a serotonin release assay, but not the standard

Question 22

What are the two forms of microangiopathic hemolytis anemias that lead to non-immune platelet destruction?

Answer 22

Thrombotic Thrombocytopenic Purpura (TTP)

Hemolytic Uremic Syndrome (HUS)

Question 23

How do you diagnose non-immune peripheral plt destruction?

Answer 23

blood smear
coags
reticulocyte count
LDH
haptoglobin

Question 24

What’s the cause of TTP?

Answer 24

either an acquired or congenital deficiency of ADAMTS13, which makes protein C unable to turn off, so you get platelet-rich thrombi throughout microvascular causing red cell fragmentation and clots

Question 25

How can you diagnose TTP?

Answer 25

red cell fragments on smear
thrombocytopenia
high LDH
low haptoglobin
measure the ADAMTS13 level, activity assay and antibody levels

Question 26

How do you treat TTP?

Answer 26

plasma exchange

Question 27

What is the most common congenital disorder of platelet function

Answer 27

vWF def

Question 28

What are causes of acquired disorders of plateet function?

Answer 28

ASA and NSAIDS
uremia
post-cardiac bypass pump
acquired vWF disease (seen with some myeloproliferative disorders like polycythemia vera)

Question 29

How can we test platelet function?

Answer 29

Don’t use a bleeding time!

We have automatic function analyzers now that basically do an in vitro bleeding time

it’s the platelet closure time (PFA-100 is the most common analyzer)

Question 30

The analyzers wont work if the platelet count is less than ___

Answer 30

90,000

Question 31

How does platelet aggregometry work?

Answer 31

it measures platelet function by measuring platelet aggregation in response to platelet agonists like ADP, collagen and ristocetin

it’s expensive and labor itnesnive so rarely used

Question 32

Why can’t you use the mean platelet volume?

Answer 32

Because platelets variably increase in size the longer they are in EDTA and no one has figured out a way to correct for this