Anaphylactoid and anaphylactic reactions to iodinated contrast material

Some adverse reactions to iodinated contrast material (ICM) are considered allergy-like, with cutaneous, cardiovascular, respiratory, and digestive sy mptoms. Allergy-like reactions are usually unpredictable. Reactions are mor e frequent with ionic than with nonionic material, but the frequency of dea ths is almost identical. In a recent study, 20 severe unexpected reactions to ICM, including 10 life-threatening reactions and one death, were investi gated by measuring mediators in blood, within the first minutes or hours of reaction. The responsible ICMs were mostly ionic materials. Histamine and tryptase release correlated with the severity of the reaction. Specific IgE against the responsible ICM was significantly higher in reactors than in c ontrols. A few patients had positive skin tests to the administered ICM, su ggesting type-1 allergic reaction. Only 2.4% and 3.1% of the cases yielded a positive IgE-RIA, in a second retrospective study which included 165 pati ents recruited during a 4-year period. In conclusion, IgE-mediated anaphyla xis is rare, but it may be one of the possible mechanisms of severe adverse reactions to ICM.