Immediate reactions to contrast media: mediator release and value of diagnostic testing.

Immediate reactions to iodinated contrast media (ICM) resembles anaphylaxis. The recent literature demonstrates that histamine is released in vivo, with a peak concentration correlating within the severity grade of the reaction. Mast cells participate in severe reactions, as shown by several authors through the release of tryptase. In patients with severe reactions, intradermal testing with immediate reading appear positive to the culprit ICM, confirming an immune mechanism. For further procedures, a strict avoidance of the culprit ICM must be observed. The injection of another ICM giving negative skin tests has proved safe in a few patients.