thrombocytopenia

Question 1

heparin induced thrombocytopenia

Answer 1

antibody to the complex of heparin and platelet factor 4 (PF4).

• platelet removal by splenic macrophages
• platelet activation –> venous and arterial thrombosis

Question 2

HIT diagnosis

Answer 2

PF4-heparin ELISA (immunoassay)
or functional assay (SRA or HIPA) - use if immunoassay or OD is indeterminate. Longer turnaround time than elisa.
if unavailable, can use optical density (OD) as surrogate for immunoassay. OD has higher false positive rate.

Question 3

HIT treatment

Answer 3

argatroban - avoid with liver dysfunction. cleared by liver. monitor aPTT
fondaparinux - avoid with renal dysfunction. cleared by kidney. No monitoring.
continue non-warfarin anticoagulation until plt > 150 then bridge to warfarin. duration 1 month vs 3 months

Question 4

Primary Thrombotic Microangiopathic (TMA) syndromes

Answer 4

ADAMTS13 deficiency-mediated TMA (TTP)
- tx with plasma exchange
shiga toxin-mediated TMA (ST-HUS)
- tx with supportive care. No antibiotics!
drug-mediated TMA: ex quinine, VEGF inhibitors
complement-mediated TMA
- tx with plasma exchange