David Green
Chicago, Illinois, United States
An infusion of iodinated contrast medium enhances the images of organs and tissues depicted by radiographic studies, and such infusions are routinely included in most of these examinations. While generally well tolerated, allergic reactions to the infusates do occur and might be severe. Therefore, persons scheduled for imaging are required to complete a questionnaire asking whether they have ever had a reaction to contrast medium. If the answer is positive, patients are required to take an anti-allergy preparation (prep) consisting of 150 mg of prednisone and 50 mg of diphenhydramine during the twelve hours before the examination. However, this prep should not be mandatory for every patient, as illustrated by the following example.
An eighty-nine-year-old woman was scheduled for a contrast-enhanced cardiac computed tomography (CT) examination. More than forty years earlier, she had developed bilateral palpebral edema immediately after an infusion of iodinated contrast given during the course of an intravenous pyelography examination. She was told she was allergic to contrast agents, and although she had several CT examinations over the next four decades, they were always performed without contrast infusion. She did have a contrast-enhanced cardiac magnetic resonance imaging (MRI) study, but MRIs use gadolinium-based contrast agents rather than iodinated media, and no signs of allergy were noted. For the planned cardiac CT scan, she completed the pre-examination questionnaire, answering “yes” to the question of whether she was allergic to iodinated contrast media.
The cardiac CT scan now ordered was needed to depict certain anatomical features used for the placement of an intracardiac device, and the administration of contrast media was an absolute requirement. Because she had answered “yes” to the question of whether she was allergic to contrast, she would have to take the allergy prep. But was it really necessary? The patient had a single allergic reaction which occurred prior to 1985. That is significant because the Food and Drug Administration approved the first low-osmolality contrast agents in 1985, and they replaced the high-osmolality media which had been associated with a much greater frequency of adverse reactions: a difference of 6–8% vs 0.2–0.7%.1 She had never been exposed to the newer contrast agents, so whether she would have an allergic reaction to them was unknown. In fact, because of the rarity of such reactions with the newer agents, allergy preps are not routinely required if there is no history of a reaction to currently used contrast media. This issue has been addressed in the radiology literature, and premedication is not recommended if there is only an isolated history of a reaction to an unknown contrast agent prior to 1985.2
The pre-examination questionnaire had no provision for patients to elaborate on their history of contrast reaction; not even to include the date of the event. Once the “yes” box was ticked, the allergy prep became mandatory. If taking the prep were innocuous, there might not be a concern about its implementation. However, the prep required ingesting 150 mg of prednisone over the space of twelve hours. Potential adverse effects associated with this steroid dose are sleep difficulty, increased appetite, stomach upset, water retention, and sudden mood changes like anxiety or agitation.[iii] While such effects might be well tolerated in young, relatively healthy individuals, they could have severe consequences in an eighty-nine-year-old frail woman with heart disease. To avoid the allergy prep, and because she had never had a reaction to the currently used contrast agents, the patient changed her answer to “no” on the questionnaire. Consequently, an allergy prep was not given, and the contrast-enhanced CT scan was performed without incident.
If radiologists are concerned about preventing reactions to contrast media, they should revise the preexamination questionnaire to better identify patients at risk. Those with a prior adverse experience should have a space to indicate when the event occurred. Other history that might be requested would be a description of the reaction, the treatment given, and, if known, the identity of the contrast agent. Such information would be extremely helpful in avoiding future reactions as well as avoiding unnecessary allergy preps.
References
- Cochran SI, Bormyea K, Sayre JW. Trends in adverse events after IV administration of contrast media. AJR 2001; 176: 1385-88.
- Wang C, Ramsey A, Lang D, Copaescu AM, Krishman P, Kuruvilla M, Mervak B, et al. Management and prevention of hypersensitivity reactions to radiocontrast media: a consensus statement from the American College of Radiology and the American Academy of Allergy, Asthma & Immunology. Radiology 2025 May; 315(2) e240100. doi: 10.1148/radiol.240100.
- Min KH, Rhee C0K, Jung JY, Suh M-W. Characteristics of Adverse Effects When Using High Dose Short Term Steroid Regimen. Korean J Audiol. 2012 Sep 20;16(2):65–70. doi: 10.7874/kja.2012.16.2.65
DR. DAVID GREEN is a Professor of Medicine Emeritus at Northwestern University. He is a graduate of Jefferson Medical College (MD), and he completed residency in Internal Medicine and Fellowship in Hematology from Jefferson and subsequently a PhD in biochemistry from Northwestern University. He is the author or co-author of more than 300 peer-reviewed scientific papers and five books.