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Flashcards in Platelets Deck (32)
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1

How much of our platelets are pooled in our spleens?

about 33%

2

What are the four major platelet tests?

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

3

What are the four GENERAL causes fo thrombocytpenia?

artifactual
decreased production
increased destruction
increased sequestration

4

What are the two GENERAL causes of thrombocytosis?

primary (neoplastic)
secondary

5

What are some of the reasons you get artifactual thrombocytopenia?

EDTA-induced platelet clumping from the test tube

clotted specimen

platelet clumping in myelodysplastic or myeloproliferative disorders

6

How can you tell if the thrombocytopenia is artifactual/

the lab's supposed to figure it out

check the perpheral blood morphology

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

7

What are some general causes of decreased PLT production?

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

8

What are some classic drugs that suppress megaK production?

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

ETHANOL

9

WHat are some immune causes of increased platelet destruction?

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

10

What are some non-immune causes of platelet destruction?

increased loss (using them all up)

increased use due to pathologic clotting (DIC)

sequestration (hypersplenism)

11

What causes immune thrombocytopenic purpura (ITP)?

presumed due to anti-platelet antibodies

associated with viral infections and autoI disorders

12

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

the bone marrow biopsy

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

13

What is the most common cause of severe neonatal thrombocytopenia?

fetomaternal platelet incompatibility

14

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

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

15

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

mom's serology

mom and dad's platelet antigen testing

genotype parents and baby

16

How do you treat neonatal purpura?

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

17

Who gets post-transfusion purpura?

HPA-1a negative individuals

18

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

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

19

Which type of hepatin has the higher incidence of HIT?

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

20

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

2-20%

21

How do we diagnose HIT now?

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

22

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

Thrombotic Thrombocytopenic Purpura (TTP)

Hemolytic Uremic Syndrome (HUS)

23

How do you diagnose non-immune peripheral plt destruction?

blood smear
coags
reticulocyte count
LDH
haptoglobin

24

What's the cause of TTP?

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

25

How can you diagnose TTP?

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

26

How do you treat TTP?

plasma exchange

27

What is the most common congenital disorder of platelet function

vWF def

28

What are causes of acquired disorders of plateet function?

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

29

How can we test platelet function?

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)

30

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

90,000