In heparin-induced thrombocytopenia (HIT type II), thrombocytopenia occurs due to:

• A Direct toxic effect of heparin on megakaryocytes reducing platelet production
• B IgG antibodies against heparin-platelet factor 4 (PF4) complexes activating platelets via FcγRIIA receptors ✓
• C Complement-mediated lysis of platelets coated with heparin-antibody complexes
• D Consumption of platelets in microthrombi due to von Willebrand factor-rich thrombi

Explanation

HIT type II is an immune-mediated disorder: heparin binds platelet factor 4 (PF4) released from platelets, and this complex is recognized by IgG antibodies. The IgG-PF4-heparin complexes bind FcγRIIA receptors on platelets, causing platelet activation, aggregation, and thrombocytopenia, paradoxically associated with thrombosis (not just bleeding). Treatment requires stopping heparin and substituting a direct thrombin inhibitor (argatroban) or fondaparinux.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.