Background: Heparin-induced delayed-type hypersensitivity reaction (HIDHR) is a rare but clinically significant adverse effect of low molecular weight heparins (LMWHs). It represents a type IV hypersensitivity reaction mediated by T lymphocytes and typically occurs 1-3 weeks after treatment initiation. Clinically, it presents with pruritic erythematous plaques at injection sites, sometimes spreading beyond. Early recognition is essential to avoid complications and to ensure safe anticoagulant substitution.