Written by Megan Hilbert
Spoon Feed
The catch-all term of “contrast allergy” needs to be carefully clarified with patients. Premedication can likely be achieved with antihistamine-only in patients that have exhibited a hypersensitivity reaction, but switching contrast agent is even better at preventing future reactions.
Let’s compare and contrast…
Contrast reactions have two categories: physiologic and hypersensitivity. Physiologic reactions are chemotoxic (or related to the molecular structure) and non-immune, are usually within 1 hour of contrast administration, are self-limited, and do not require future premedication. Hypersensitivity reactions are immune related and can be immediate (within 1 hour) or delayed (hours to days). These reactions can be rated mild, moderate, or severe (severe is rare, 0.005–0.06%). Prior history of hypersensitivity reaction confers a 5–6-fold increase in recurrent risk.
A nice graphic from the paper:
This was a comparison of guidelines published in 2025 from Canada, the USA, and Europe. Some central tenets are the same. Here are the high-yield points:
- It is a myth that shellfish and iodine allergies are associated with contrast media reactions. Iodine is not an allergen (it is critical to bodily functions!), and we should not use the term “iodine allergy.” IgE allergies to shellfish are usually due to tropomysin, not iodine.
- It is extremely important to gather a pertinent history: agent, timing and severity of reaction.
- Corticosteroids have limited use in acute anaphylaxis management, and the research does not show reduction in biphasic reaction.
- Serum tryptase biomarker testing does not change acute management but can help provide pertinent information to an allergist, to which we should be referring patients.
- Mitigating future hypersensitivity reactions can be achieved in two ways: changing the contrast agent or pharmacologic premedication. Antihistamine premedication has been shown to reduce risk (OR 0.53, 95%CI 0.33-0.86) and recurrence rate from 16.6% to 10.7% (OR 0.57, 95%CI 0.44–0.73). Adding corticosteroid does not confer additional benefit, and the literature is outdated. Our rapid premedication in the ER (think 5 hours rather than 13) “offers a shorter delay to imaging rather than superior protection.” Switching agent, however, has been shown to reduce risk of breakthrough reaction by 61% (risk ratio 0.39, 95%CI 0.24–0.58)!
How will this change my practice?
I have some improvements to make in my practice. First, I will refer patients with a contrast reaction to an allergist, though I doubt my sites have the ability to send a serum tryptase. Secondly, I will clarify reported contrast reactions and parse whether physiologic or hypersensitivity. Finally, I plan on reaching out to my radiology colleagues about availability of other contrast agents at my sites. I doubt I can remove corticosteroids from premedication regimens, but I can at least know the literature doesn’t necessarily support its inclusion.
Source
Emergency medicine updates: Contrast media hypersensitivity. Am J Emerg Med. 2026 Oct 8:S0735-6757(26)00521-8. doi: 10.1016/j.ajem.2026.09.057. Epub ahead of print. PMID: 42879941.
