Mechanisms of severe, immediate reactions to iodinated contrast material.

PURPOSE: To measure and elucidate the mechanisms of presumed mediators of unexpected severe, immediate reactions to iodinated contrast materials. MATERIALS AND METHODS: In a multicenter study, 20 patients with mild to severe reactions to iodinated contrast material and 20 control subjects without reactions were evaluated. Ionic contrast material was associated with 18 (90%) of 20 reactions. Concentrations of plasma histamine, tryptase, urinary methylhistamine, specific immunoglobulin E (IgE) against ioxitalamate or ioxaglate, and the anaphylatoxins C3a and C4a were measured with radioimmunoassays; complement C3 and C4 levels were measured with nephelometry. RESULTS: Histamine levels were increased in 14 patients; tryptase levels, in 16; and methylhistamine levels, in six. Histamine and tryptase values correlated with the severity of the reaction (P < .02 and P < .004, respectively). Significantly higher levels of specific IgE against ioxaglate (P < .005) and ioxitalamate (P = .045) were found in patients. No differences were found for complement fractions. Skin test results in two patients with life-threatening reactions were positive for the administered contrast material. CONCLUSION: Histamine release and mast cell triggering are related to severe reactions. An IgE-related mechanism is strongly suspected. Radiologists should be trained to identify and treat anaphylactic shock in patients who react to iodinated contrast material.