LM 6.3: Disorders of Hemostasis Flashcards
what platelet count classifies as thrombocytopenia?
<100,000 platelets/mL
what platelet count classifies as thrombocytosis?
> 600,000 platelets/mL
what is thrombocytopathy?
disorders of platelets function
what do you usually see in the history of someone with a platelet disorder?
- mucocutaneous bleeding
- heavy menses
- alcohol
- family history of bleeding
what do you see during the physical exam of someone with a platelet disorder?
- petechia
- purpura
- enlarged spleen
what are the categories of disorders of platelet function?
- congenital
- acquired
- due to drug exposure
- due to systemic disease
what tests do you do for platelet function disorders?
platelet count would be normal!!
but the platelet function screening tests would be abnormal
- platelet aggregation study
- platelet electron microscopy
- thomboelastography
what are the types of congenital platelet storage pool disorders?
- deficiency of the storage granules of the platelets
2. malfunction of the granule secretory mechanism (aspirin-like defect)
which diseases are congenital platelet receptor disorders?
- Glanzmann’s thrombasthenia
2. Bernard Soulier syndrome
what is Glanzmann’s thrombasthenia?
deficiency of the IIb/IIIa receptors on the platelet membrane
this is the receptor for fibrinogen
what is Bernard Soulier syndrome?
deficiency of the Ib receptor
this is the receptor for von willebrand factor
which medications can cause acquired disorders of platelet function?
- non steroidal anti-inflammatory drugs all reduce platelet function
the effect of aspirin is irreversible so 7-10 days are required for an entirely new population of normally functioning platelets to be present –> 7-10 days is the lifespan of a platelet
- Clopidogrel (Plavix) and other anti-platelet drugs are also irreversible
which systemic disorders can cause acquired disorders of platelet function?
- uremia
- cardiopulmonary bypass
- paraproteinemia
- disseminated intravascular coagulation (DIC)
- myeloproliferative and myelodysplastic disorders
treatment of these underlying disorders is the best way to correct the platelet dysfunction
why can uremia cause acquired disorders of platelet function?
uremia = severe kidney dysfunction
there can be an increased risk of bleeding due to an accumulation of toxic metabolites
best therapy is hemodialysis
what is pseudo thrombocytopenia?
aka EDTA induced thrombocytopenia
a disorder due to autoantibodies int he patient that cause the patient’s platelets to clump in the test tube used for the CBC (EDTA is the anticoagulant in the tube!)
this causes an artificially low platelet count even though the real platelet count in the patient is fine
you would need to get another sample of blood but use heparin in the tube instead of EDTA to confirm that the platelet count is really normal
what are the various mechanisms of thrombocytopenia?
- decreased production of platelets in the bone marrow - like from toxic drugs
- dilution of platelets in the peripheral blood - like from a transfusion of platelet-poor blood
- maldistribution of platelets - like in patient with large spleens
- excessive consumption/destruction of platelets in circulation - like in autoimmune thrombocytopenia
what are the clinical clues that suggest thrombocytopenia due to reduced platelet production?
- normal sized platelets on blood smear
- anemia or abnormal WBCs might be seen on blood smear
- significant bleeding in patient
what could cause thrombocytopenia due to reduced platelet production?
- chemo
- alcohol
- drugs
- HIV
- HepC
- parvovirus
these all suppress platelet production
when should you avoid a platelet transfusion?
if there’s splenomegaly
infusing with platelets won’t help because they’ll all just pool in the large spleen
what clinical clues would suggest thrombocytopenia due to increased consumption/destruction of platelets?
- large platelets on the blood smear
- bleeding is often less than expected considering the platelet count
what are some disorders that are associated with thrombocytopenia due to increased consumption/destruction of platelets?
- autoimmune disorders like immune thrombocytopenia purpura (ITP)
- viral infections, especially in kids
- HIV positive patients
- heparin induced thrombocytopenia
what is adult ITP?
Immune thrombocytopenic purpura
- more common in women
- mucocutaneous bleeding
- NO splenomegaly
- platelets are coated with antibodies
what is the treatment for adult ITP?
- corticosteroids
- high dose immunoglobulin
- rituxan
- splenectomy
initial therapy should be steroids - only use high dose immunoglobulin if there is severe thrombocytopenia or life-threatening bleeding
second line defense is Rituxan if steroids don’t increase platelet count
what is childhood ITP?
usually happen after a viral illness
the antibody is usually against a viral protein antigen and the platelets become sensitized by the viral antigen absorbed on the platelet membrane or by the viral/antibody complexes on the platelet membrane
usually self limiting and resolves by itself in 2-3 months
avoid splenectomy
