Chapter 140 Disorders of Platelets and Vessel Wall Flashcards
Cutoff for thrombocytopenia?
Platelet <150,000/uL
Normal 150,000-450,000
Major regulator of platelet production
Thrombopoietin (TPO)
Synthesized in the liver
Increased in inflammation, by IL-6
Life span of platelets?
7-10 days
1/3 of platelets reside in the spleen
Next step in the algorithm if thrombocytopenia is accompanied by abnormal Hgb and WBC?
Bone marrow examination
Exception: Isolated thrombocytopenia in patients >60 years, also do bone marrow studies to rule out myelodysplasia
Pinpoint non blanching hemorrhages that are usually the sign of decreased platelet NUMBER and not platelet dysfunction?
Where are these hemorrhages usually seen?
Petechiae
Appear in areas of increased venous pressure - ankles and feet
Common bacterial or viral infections that cause infection induced thrombocytopenia?
Gram negative bacteria
Infectious mononucleosis
HIV
Mainstay work up for diagnosis of IIT?
Bone marrow examination
Blood cultures
When does thrombocytopenia occur when exposed to platelet IIB/IIIA inhibitory drugs?
Examples of these drugs?
Within 24 hours of initial exposure
Abciximab
When does thrombocytopenia occur in drug induced thrombocytopenia?
After initial exposure, median of 21 days
Or upon reexposure
Resolves 7-10 days after drug withdrawal
Two main differences of HIT from other drug induces thrombocytopenia?
Thrombocytopenia not severe
HIT is not associated with bleeding, it actually markedly increases risk for thrombosis
Pathogenesis of HIT?
Development of antibodies to heparin/PF4 complex
HIT is more common after exposure to: UFH or LMWH?
More common in UFH exposure
After 5-14 days of exposure
Diagnostic algorithm for HIT (4T’s)
Thrombocytopenia
Timing of platelet count drop
Thrombosis
Localized skin reactions
How long do heparin/PF4 complexes stay in circulation before disappearing?
~100 days following a prior exposure
Rare type of HIT that occurs after all heparin has been stopped, beyond 14 days since last exposure
Delayed onset HIT
Heparin/PF4 antibody testing is markedly positive
Diagnostic test for HIT that has high specificity but low sensitivity, may be falsely high in patients who have undergone cardiopulmonary bypass surgery?
IgG specific ELISA to PF4 complex
Diagnostic test for HIT which measures the ability of the patient’s serum to activate platelets in the presence of heparin?
Serotonin release assay (a platelet activation assay)
Lower sensitivity, higher specificity than ELISA
Most common complication of HIT even after discontinuation of heparin?
Thrombosis, venous and arterial
What imaging modality is recommended to evaluate patients suspected of having HIT?
Duplex scan of the lower extremities to work up for thrombosis
Which direct thrombin inhibitors (DTI) can be used as alternative for heparin in HITT?
Argatroban
Lepirudin
Others not approved by FDA:
Fondaparinux
Bivalirudin
Alternative treatment for HIT which is a mixture of glycosaminoglycans with anti Xa activity?
Danaparoid
If anticoagulation is needed due to high risk of thrombosis in HIT, what drug can be given in place of heparin?
Warfarin, usually for 3-6 months
Introduction of warfarin alone may precipitate thrombosis due to clotting activation and reduced protein C and S
Should be overlapped with DTI to lessen prothrombotic state
What underlying disorders can cause secondary ITP?
Autoimmune disorders such as SLE
Infections such as HIV and Hepatitis C
Expected results of platelet count and blood smear in ITP?
Very low platelet count
Normal peripheral blood smear
