EXAM #1: THROMBOCYTOPENIA Flashcards
What is the definition of thrombocytopenia?
Platelet count less than 150,000/microliter
Describe the appearance of platelets on PBS.
- Round- oval
- Blue-gray
- 1/3 the size of a RBC
- Anuclear
Where are platelets produced? What are they released from?
- Produced in the bone marrow
- Megakaryocytes
What regulates platelet production? Where is this factor synthesized?
Thrombopoietin, which is synthesized in the liver
What receptor is activated after binding of Gp1b to vFW?
GpIIb/IIIa, which binds fibrin
What are the three underlying causes of thrombocytopenia?
1) Underproduction
2) Destruction
3) Sequestration
What are some of the infectious causes of platelet underproduction?
1) HIV
2) Parvovirus B19
What is the most common cause of underproduction of platelets from the bone marrow?
- Chemotheraputic agents
- Alcohol
If the MCV is greater than 115 or more, what should you think?
Megaloblastic anemia i.e. B12 or Folate
What is the mechanism of thrombocytopenia in pernicious anemia?
B12 is necessary to DNA synthesis, i.e. synthesis of platelet precursors
What will the megakaryocyte levels be in pernicious anemia?
Normal to increased numbers for megakaryocytes
What cancer is associated with pernicious anemia?
Gastric carcinoma
How is pernicious anemia managed?
B12 supplementation
What is pseudothrombocytopenia?
Platelet aggregation or clumping in vitro leads to a low count
What triggers pseudothrombocytopenia? How do you correct for it?
- EDTA
- Recheck with citrated or heparanized blood tube i.e. purple tube
What is ITP?
Idiopathic or Immune Thrombocytopenic Purpura
Describe the pathology of ITP.
- Accelerated destruction of platelets b/c antibody coated platelets are destroyed by macrophages in spleen
- GpIIb/IIIa
- Normal or increased megakaryocytes
- Diagnosis of exclusion*
What is the typical clinical presentation of ITP?
Often asymptomatic with SEVERE thrombocytopenia
Some have purpura, petechiae…etc. but LIFE-THREATENING bleeding is RARE
What is the treatment for ITP?
- Observation
- Steroids
- IVIG–coat receptors with something other than antiplatelet antibody
- Rituximab
- Thrombopoetin
- Splenectomy
What are the two classes of platelet destruction?
- Immune-mediated
- Nonimmune-mediated
List the causes of immune-mediated platelet destruction.
- ITP
- HIT
- Post transfusion purpura
- Medications
- Antiphospholipid antibody syndrome
List the causes of nonimmune-mediated platelet destruction.
- DIC
- TTP/HUS
- HELLP Syndrome
- Gestational Thrombocytopenia
- Mechanical Destruction
- Localized intravascular coagulopathy
What is HIT?
Heparin Induced Thrombocytopenia
- Immune mediated destruction of platelets
- Antibodies to heparin AND platelet-specific PF4 complex
- Activates platelets and leads to thrombosis
What form of Heparin has a lower risk of HIT associated?
LMWH
How is HIT managed?
1) STOP heparin
2) Use alternative anti-coagulant
Can you use Heparin again in a patient that has developed HIT?
Yes, if they have been Heparin free for 6 months
What does jaundice not involving the sclera indicate?
NOT hyperbilirubinemia
What causes sequestration of platelets?
Splenomegaly leads to splenic sequestration
- Portal HNT
- Hereditary spherocytosis
- CML
- Hairy cell leukemia
- MALT lymphoma
How do you evaluate thrombocytopenia?
1) HIP and PE
2) Lab eval
3) Bone marrow biopsy
When is bone marrow indicated?
1) Multiple cell lines involved
2) Greater than 60 with isolated thrombocytopenia
3) When empiric therapy is unsuccessful
What is the formula for platelet transfusion?
1 unit= increase in 5,000
Normal 6-pack is 30,000
When is platelet transfusion a BAD idea?
ITP
HIT
