LMWH is associated with heparin-induced thrombocytopenia (HIT) incidence compared with UFH?

• A. It is more common with LMWH
• B. It is less common with LMWH
• C. It is not associated with LMWH
• D. It is the same as UFH

Answer: (B)

The key concept is that the risk of heparin-induced thrombocytopenia is lower with low-molecular-weight heparin than with unfractionated heparin. HIT is an immune reaction where antibodies form against complexes of heparin and platelet factor 4, activating platelets and causing thrombocytopenia with a risk of thrombosis. Unfractionated heparin presents a broader mix of longer chains that form larger, more immunogenic PF4-heparin complexes, so HIT occurs more frequently. Low-molecular-weight heparin, being a smaller fragment with more predictable pharmacokinetics, forms less immunogenic complexes, leading to a reduced incidence of HIT. Note that HIT can still occur with LMWH, so clinicians remain vigilant and may switch to a non-heparin anticoagulant if HIT is suspected.