It depends on which part of your body is being scanned. Although rare, the contrast medium Involved in a CT scan poses a slight risk of an allergic reaction. Most reactions are mild and result in hives or itchiness. For people with asthma who become allergic to the contrast medium, the reaction can be an asthma attack.
In rare instances, an allergic reaction can be serious and potentially life-threatening — including swelling in your throat or other areas of your body. If you experience hives, itchiness or swelling in your throat during or after your CT exam, immediately tell your technologist or doctor.
If you’ve had a reaction to a contrast medium in the past, and you need a diagnostic test that may require a contrast medium again, talk to your doctor. Be sure to let your doctor know if you have kidney problems since contrast material that’s injected into a vein is removed from your body by your kidneys and could potentially cause further damage to your kidneys.
If you have had a prior reaction to contrast media or have asthma or allergies, there’s an increased risk of a reaction to the contrast medium. Diabetes, asthma, heart disease, kidney problems or certain thyroid conditions may increase your risk of a reaction to contrast media.