Abstract
Ferumoxytol is a newly approved preparation of intravenous iron with a modified dextran shell that is thought to confer upon it a low immunogenic potential. Serious adverse reactions have been very uncommon in clinical studies, but these studies excluded patients with prior adverse reactions to other preparations of intravenous iron. Furthermore, the reactions were classified clinically. We report on a patient with a history of hypersensitivity to iron dextran who experienced an anaphylactic reaction after receiving ferumoxytol. Laboratory testing revealed an elevated serum tryptase level, confirming mast cell activation. This is the first laboratory-proven case of anaphylaxis related to ferumoxytol.