“What if I'm allergic to contrast?”
Many years ago I had some minor itching after receiving CT contrast. Now I am considered to be allergic to the contrast. What if I need another CT? What will happen?
12 Answers
Allergy to contrast must be documented on the CT report so your physician can advise premedication on your next CT scan. Maybe even steroids in advance depending on the severity of the allergic reaction.
It is not uncommon to have an iodine allergy during a CT scan. This not preclude you from having CT scan. You can be premedicated before the procedure to prevent an allergic response. Benadryl and steroids are common medications used for premedication. Please let everyone know that you have a contrast allergy before any CT scans so as to prevent another reaction.
Many years ago, contrast materials were called ionic contrast. Currently, the contrasts that are used are called non-ionic contrast. They seem to have less potential for causing reactions. To be safe however, it would probably be advisable to take some sort of prednisone prep prior to having a contrast that study, just to be safe. Your radiologist should know a particular prep type which they are comfortable with.
New contrast agents are much more safe, you should take 24 hours of steroids, 25mg prednisone every 6 hours for 24 hours and then bolus you with 4mg iv decadron and 50 mg Benadryl immediately prior to your IV contrast.
If you have a true allergy to contrast you will need to be premeditated with an oral steroid and antihistamine. There is a set protocol that your referring physician can obtain so that he or she can give you the prescription you require prior to a contrast study.
There are protocols to premeditate patients with contrast allergies using steroids and antihistamines. Should be safe.
Contrast allergies should always be taken seriously. While most people have a similar level of reaction, there are cases where a person with a minor allergy at one session had a major reaction (as in airway compromise) at a later setting. If you need a CT with contrast in the future, you should ask your primary care physician to prescribe the pre-treatment protocol that is in place at your local hospital or imaging center. This usually involves a short course of steroids prior to the administration, which stops the allergic reaction from even starting.
Barry Aubrey Sacks
Radiologist
If you have had a previous contrast allergy, the CT scan can still be done with intravenous contrast as long as the patient has been pretreated with Cortisone. This is usually started the day before and the day of the procedure. There are a few different protocols using slightly different doses of prednisone and Benadryl. Either you or your doctor can discuss this with the local radiologist doing the CT scan.
You would probably receive a non-contrast CT if that would supply enough information. Otherwise, depending on what area was to be studied, an ultrasound or an MRI might be attempted. If the Enhanced CT was absolutely necessary and if you were willing, an enhanced CT could be performed performed after being treated with steroids.
You could get premedicated prior to the exam or you could try the exam without and then be observed for 1/2 hour after. Sometimes people who had a minor reaction get repeat exams and do fine. I would discuss with your doctor prior to the exam.
Dr Cox
Dr Cox
Many years ago the iodinated contrast used in CT was different. The modern contrast has less contrast reactions. If you are concerned, you can take 50 mg of Benadryl before the study. Your doctor may also suggest a short course of steroids if you previously had a bad reaction (difficulty breathing).
At the time of the CT, the technologist will ask you questions about your contrast allergy. IF the allergy needs to be treated, the technologist will obtain an authorization from the radiologist who will then give you a prescription for steroids and anti-inflammatories which you take prior to undergoing the CT scan. We handle this issue very routinely.
