Adverse skin reactions to low molecular weight heparins: frequency, management and prevention.

Adverse skin reactions to low molecular weight heparins (LMWH) are rare even though their true incidence is probably underestimated because of underreporting. These reactions may occur as an urticarial rash, presumably due to local histamine release or have the features of a classic type I immediate hypersensitivity reaction. They can also present as skin necrosis often due to vasculitis (type III Arthus reaction) or heparin-induced thrombocytopenia. Erythematous, well circumscribed lesions without necrosis are usually secondary to a delayed type IV hypersensitivity reaction.