Injectable dye, also referred to as radiocontrast media (RCM), is used in a wide variety of x-ray studies, including angiograms, computed tomography (CT) scans, and intravenous pyelograms. Reactions to RCM have been reported to occur in up to 13% of patients receiving intra-venous contrast. More often than not, the reactions are mild and consist of flushing, dizziness, and nausea. Less than 2% of people receiving contrast will have more severe reactions, which may include diffuse hives, vomiting, and occasionally throat swelling or a drop in blood pressure.
People who are at higher risk for reactions to RCM include women, the elderly, those with past reactions to RCM, patients with histories of asthma, allergies, and heart disease, and people taking beta-blocker drugs. Contrary to popular belief, seafood allergy is in no way connected to RCM reactions. Therefore, if a person has a history of RCM sensitivity, it does not suggest that he or she will be allergic to shrimp or shellfish, or vice versa. The diagnosis of RCM is made strictly based on history, as there is currently no test available that accurately predicts the occurrence of reactions.
Prevention of future reactions is the single most important task for the patient and physician. For future procedures involving RCM, the radiologist should use low-ionic, low-osmolarity contrast media in place of high-osmolarity media. In addition, the use of medications, such as prednisone and diphenhydramine, prior to the administration of RCM may help greatly in reducing the incidence and severity of reactions.