Flashcards in Platelets Deck (32)
How much of our platelets are pooled in our spleens?
What are the four major platelet tests?
bleeding time (or new alt)
blood smear morphology
What are the four GENERAL causes fo thrombocytpenia?
What are the two GENERAL causes of thrombocytosis?
What are some of the reasons you get artifactual thrombocytopenia?
EDTA-induced platelet clumping from the test tube
platelet clumping in myelodysplastic or myeloproliferative disorders
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
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
What are some classic drugs that suppress megaK production?
WHat are some immune causes of increased platelet destruction?
drug-induced immune thombocytopenia
What are some non-immune causes of platelet destruction?
increased loss (using them all up)
increased use due to pathologic clotting (DIC)
What causes immune thrombocytopenic purpura (ITP)?
presumed due to anti-platelet antibodies
associated with viral infections and autoI disorders
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
What is the most common cause of severe neonatal thrombocytopenia?
fetomaternal platelet incompatibility
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
How do you make the diagnosis of neonatal purpura in caucasians?
mom and dad's platelet antigen testing
genotype parents and baby
How do you treat neonatal purpura?
Prenatal IVIg/G or transfuse infant with ABO compatible/HPA-1a negative platelets
Who gets post-transfusion purpura?
HPA-1a negative individuals
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
Which type of hepatin has the higher incidence of HIT?
bovine is a higher molecular weight, so seems to bind up more PF4
What percentage of patients who receive unfractionated (mixed) heparin will develop HIT?
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
What are the two forms of microangiopathic hemolytis anemias that lead to non-immune platelet destruction?
Thrombotic Thrombocytopenic Purpura (TTP)
Hemolytic Uremic Syndrome (HUS)
How do you diagnose non-immune peripheral plt destruction?
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
How can you diagnose TTP?
red cell fragments on smear
measure the ADAMTS13 level, activity assay and antibody levels
How do you treat TTP?
What is the most common congenital disorder of platelet function
What are causes of acquired disorders of plateet function?
ASA and NSAIDS
post-cardiac bypass pump
acquired vWF disease (seen with some myeloproliferative disorders like polycythemia vera)
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)