Allergic heparin hypersensitivity – recommendations for diagnostic work up and patient management

Abstract

Heparins are unproblematic drugs from an allergist’s perspective, since despite frequent application heparin hypersensitivity is quite rarely in clinical routine. This article provides an overview of selected scientific articles and is based on a literature search in PubMed and specialist databases. Most commonly, heparin allergic patients develop lymphocyte-mediated, eczematous local reactions directly at the injection sites (usually on the lower abdomen) hours to days after initiating regular subcutaneous heparin injections. The high sensitivity of skin-prick and intradermal testing procedures means that subcutaneous provocation tests are seldom necessary for diagnosis. The “compartment allergy” phenomenon is a particular feature of heparin-induced local allergic reactions. Here, the route of application determines whether an allergic inflammatory reaction develops. In case of heparin-allergic individuals, injections into the subcutaneous tissue cause eczematous plaques, whereas intravenous injections or infusions are well tolerated. Since the introduction of low molecular weight heparin preparations, the incidence of potentially life-threatening heparin-induced thrombocytopenia caused by activating IgG (Ig: immunoglobulin) antibodies against heparin-platelet factor 4 (PF4) complexes on platelet membranes has declined. IgE-mediated heparin allergy with immediate-type anaphylactic reactions seems to be extremely rare.