Heparin-Induced Thrombocytopenias

(Chest 2012;141:e495S; NEJM 2015;373:252)

Type I Heparin-Induced Thrombocytopenias(not clin. signif)

• Direct effect of heparin (non-immune)
• Incidence 10-20%
• After 1-4 d of heparin therapy
• Platelet nadir: >100,000/µL
• Sequelae: None
• Can continue heparin and observe

Type II Heparin-Induced Thrombocytopenias (clinically significant HIT)

• Immune (Ab)-mediated IgG against plt factor 4-heparin complex
• 1-3% with UFH, 0-0.8% LMWH
• After 4-10 d, but can occur in <24 h if prior exposure w/in 100 d (persistent Ab). Postop highest risk. Can occur after heparin d/c.
• ~60,000/µL, ↓ >50%
• Thrombotic events (HITT) in 30-50%
• Discontinue heparin
• Consider Alternative anticoagulation
• Pathophysiology-Heparin-Induced Thrombocytopenias

Further Detail

• Diagnosis of heparin-induced thrombocytopenia
• Evaluation of Suspected HIT (“4T’s”)
• Treatment of HIT (type II)

H/o HIT

if PF4 Ab ⊖ or SRA ⊖ (typically >100 d after dx) → may consider re-exposure to UFH (eg, for surgery); HIT recurrence low but can be seen (Blood 2014;123:2485)

• 👉 CXCL4