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BackTable / VI / Article
Contrast Dye Allergy: Call Iodine Allergy What It Is
Gabrielle Gard • May 5, 2022 • 11.8k hits
Despite recent advances in our understanding of contrast allergies, the term "iodine allergy" is still used to describe contrast dye allergy, Betadine soap allergy, and even shellfish allergy. However, all of these allergic conditions are incorrectly classified as iodine allergies according to Radiologist Dr. Cullen Ruff.
Dr. Ruff suggests that the term "iodine allergy" should no longer be used in the medical field as patients are not allergic to the iodine itself, but rather to some other component in the contrast agent. Furthermore, some patients may have severe allergies to other contrast dyes, such as gadolinium contrast allergy. These facts underscore the importance of understanding the specific allergenic contents of different contrasts and documenting them accordingly for patients.
Dr. Ruff shares his expertise on contrast dye allergies and the true nature of so-called iodine allergy on the BackTable Podcast. We’ve provided the highlight reel in this article, and you can listen to the full podcast below.
The BackTable Brief
• Compared to the older ionic agents, newer nonionic agents are less allergenic and better tolerated. Dr. Ruff suggests switching to these contrast agents to lower the chance of inducing a contrast dye allergy.
• "Iodine contrast allergy” is actually a misnomer according to Dr. Ruff. Allergic responses to iodine itself have been disproven by various studies.
• While allergies to Betadine soap (an iodine-based soap) and shellfish are also considered “iodine allergies,” this labeling is inaccurate because the individuals are not allergic to the iodine itself but to other agents within these materials.
• While a gadolinium contrast allergy is quite rare, certain agents can result in serious conditions, such as nephrogenic systemic fibrosis. This demonstrates the importance of increased awareness of specific contrast agents amongst healthcare providers and patients, especially when an allergy is present.
Image provided by Dr. Aaron Fritts.
Table of Contents
(1) Contrast Dye Allergies or Allergic-Like Reactions?
(2) Iodine Contrast Allergy: A Well-Established Misnomer
(3) Gadolinium Contrast Allergies: Rare but Serious
Contrast Dye Allergies or Allergic-Like Reactions?
While allergies often present differently for each patient, Dr. Ruff distinguishes allergic-like reactions from contrast dye allergies. Dr. Ruff mentions that reactions such as warmth, flushing, and nausea are allergic-like reactions that are common side effects to the older, ionic agents. Meanwhile, Dr. Ruff discusses that hives or rashes constitute a mild contrast allergy while difficulty breathing and airway compromise are severe contrast allergy. Because they are less allergenic and better tolerated, nonionic agents are Dr. Ruff’s preferred contrast agents to lower the chance of inducing a contrast dye allergy.
[Dr. Christopher Beck]:
Can you talk about the difference between what some people may qualify as an adverse reaction to contrast versus like the allergic or allergic-like reaction?
[Dr. Cullen Ruff]:
Absolutely. So the older agents that were around for decades, the older ionic ones tended to first of all, be a little more allergenic, still a low percentage, but they also had a more common rate of having a physiologic symptomatic reaction, and that could be a feeling of warmth or flushing. Some people got nauseated, so it would induce vomiting sometimes. Those type of sensations, which are not pleasant, and I can understand why the patients might not want to receive it again, but those are not allergic-like reactions. They were simply side effects, physiologic reactions from the medication itself. Remember contrast is not a single drug, it's a drug class, and the non-ionic agents first started coming out in 1985, when the FDA first approved it, and if you don't mind my using trade names, just because it's what more of us are familiar with. I don't mean to be commercially biased, I'm treating them all equally, but Iohexol or Omnipaque was the first to get FDA approval, and then there have been several other nonionic, low osmolar agents or hyperosmolar agents come out since then, and these tend to be less allergenic and also better tolerated by the patient.
[Dr. Christopher Beck]:
Because I read your paper that you had sent to me, so 85 is kind of a cutoff point, would you say? So when you're talking to patients about their allergic reactions and they said, “You know what, Doc, I had an allergic reaction to contrast where XYZ happened to me in ‘75.” There's a big difference between that description and saying, “Hey, my throat closed up after had a CT scan last year.”
[Dr. Cullen Ruff]:
That's correct, because we know that if it was before 1985, that it had to be one of the older ionic agents that are not commonly used anymore. And in fact, even though the FDA approval happened in 1985, the use of ionics persisted well into the early two thousands because those agents were cheaper. And I know my own practice routinely used an old ionic agent until the early two thousands, until we finally realized let's just do the right thing, even if it costs a little more because it was better for the patients, and it was better for the workflow of the technologists. And gradually these, I think in most places, the old ionic agents have been phased out.
[Dr. Christopher Beck]:
Yeah. So that was actually one of my next questions. I know we can't speak to some places all around the world and not every practice, but is it safe to assume that in this day, maybe within the last decade, that if you're dealing with a contrast reaction, from a CT scan or something, that it's a non-ionic compound?
[Dr. Cullen Ruff]:
That's my belief in our country, yes.
[Dr. Christopher Beck]:
All right, so let's also talk a little bit about the range of allergic-like reaction you can have because I think there's anything from as severe as anaphylactoid, patients with difficulty breathing and airway compromise, to patients with developed hives a week after the contrast administration. Can you talk about the spectrum of which we can see allergic-like reactions?
[Dr. Cullen Ruff]:
Sure, well hives or some sort of rash that is the most common reaction. and it's usually not days later, it usually occurs within the moments after the injection. There can be delayed presentations, but most of the time it's going to be while the patient is still in the office. If that's all it is, and there are no issues with breathing, then that's considered a mild reaction, and the patient, is certainly eligible to have another injection in the future. But as we're going to get into, we'll talk about how you handle patients who have had prior allergic reactions. Less commonly you get into patients who have a little trouble breathing. There may be changes in blood pressure or heart rate, and then the most severe being the anaphylactoid throat closure.
[Dr. Christopher Beck]:
And I think it's also worth mentioning with adverse reactions that vasovagal reactions are fairly common, so hypotension, bradycardia can occur. And would you say that would be more common than these allergic-like reactions?
[Dr. Cullen Ruff]:
Oh, I think so. The allergic-like reactions vary depending on what study you look at.
[Dr. Christopher Beck]:
Right. It's hard to narrow down on exactly how common they are.
[Dr. Cullen Ruff]:
It really is, and part of that is, as we're going to discuss, because of the confusion about, contrast allergies that not only patients have, but their referring physicians and even technologists and radiologists.
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Iodine Contrast Allergy: A Well-Established Misnomer
Dr. Ruff describes the origin of the misnomer that is “iodine contrast allergy.” Instead of elucidating the allergen within the iodinated contrast, it has been common practice to attribute the contrast dye allergy to the iodine itself, which is just part of the component molecule. In fact, Dr. Ruff suggests that the iodine contrast allergy term should no longer be used in the medical field because a true iodine allergy has been disproven by various studies over the years.
[Dr. Christopher Beck]:
So what are some of the common misconceptions about contrast dye allergies or “iodine allergies,” and how do we tease that apart from just adverse reactions? And then, what I will set you up for later is then we'll go back and talk about, how we can talk about not just like contrast reactions as a class, but zero in on contrast reactions specifically to what agent you had.
[Dr. Cullen Ruff]:
Sure. Well, the way I like to start looking at this is a hypothetical scenario, which sounds ridiculous, but I think it brings home the point. Let's take one of the oldest antibiotics around and that's penicillin G. Back since the thirties or forties, if someone has an allergy to penicillin G, you put that in their medical record as a listed allergy. It would never occur to someone to say, “Well, they're allergic to antibiotics and you know what antibiotics contain carbon. Why don't we just call it a carbon allergy, even though that's not really the component of the molecule that they're allergic to, but let's just call it that for slang.” That sounds so ridiculous, but unfortunately that's precisely what we've done in the field, and this started long before you and I were born. When people, instead of calling the contrast allergen by name, lump it together as a class of contrast agent allergy, and then use slang of iodine, even though iodine is a component of the molecule, but not what the actual allergen is.
[Dr. Christopher Beck]:
So what is there about iodine allergies? Like when someone said that I have an iodine allergy, that's really a misnomer, right?
[Dr. Cullen Ruff]:
The term iodine allergy needs to be removed from our medical vocabulary, and there have been studies for years that have come out, disproving the claim of an iodine allergy. And in fact, only within the past week or two, since this podcast was already arranged, there was a really important study that came out, in the American Journal of Health-System Pharmacy that looked at 70 years worth of history and basically discredited any claim that iodine itself is part of the allergen. We know that iodine is a mineral that we all need to live. It's so important that it's put into our salt supply so that people don't have iodine deficiency. It's in every multivitamin that people are going to take. And iodine is a component of our thyroid hormone, which regulates our cellular metabolism. So we all need it to live. And therefore it's nonsensical to say that somebody can be allergic to it. And then the problem comes not just when you use the term iodine as a slang to refer to iodinated contrast in general, but people use the term iodine allergy to refer to at least two other things that are completely unrelated to contrast. One of those is iodine based soap, which people can have a skin allergic-like reaction to, but it's not to the iodine itself, it's a greater part of the molecule. And then the other term that people use is for a shellfish allergy. Some people still use the slang term iodine to mean shellfish, and I'm not really sure how that ever came about. But food allergies, whether it is shellfish, dairy, peanuts, or gluten, those tend to be protein allergies. And in case of shellfish, it's believed to be a protein called tropomyosin, but these allergies have nothing to do with each other. We don't, I don't mean to sound flippant or glib, but I've never worked in a radiology department that offered shrimp tacos after the CT injection was done. We're not giving people anything that is shellfish-based, and the Betadine soap and the iodine based soap is unrelated as well. Which is why I think the term iodine allergy needs to actively be removed from all medical vocabulary and from electronic medical records as a valid allergy choice.
[Dr. Christopher Beck]:
And so also, just touching back about that shellfish allergy, just to unwind that a little bit more. So if someone has a shellfish allergy, I think this is pretty commonly known, but you can never be sure. If you have a shellfish allergy, it doesn't even predispose you to an allergic reaction to contrast materials, right?
[Dr. Cullen Ruff]:
That is correct. So one of the best references is the ACR American College Radiology Manual on Contrast Media, which everyone can access online and it's updated just about every year. It's an excellent resource, has a lot of good references and that manual on contrast media has followed this policy for some time. You don't take anybody with a reported shellfish allergy and treat them any differently with regard to a contrast injection, as long as they've never had an actual contrast injection, you treat them the same as everyone else.
[Dr. Christopher Beck]:
Got it. And the same thing with Betadine. So if someone's said, “I had a surgery a year ago, they used Betadine. It broke me out terribly.” You still treat that person with the same risk profile as someone who has had no reactions to iodinated contrast.
[Dr. Cullen Ruff]:
That's absolutely correct. They're unrelated substances. They have nothing to do with each other.
Gadolinium Contrast Allergies: Rare but Serious
While some patients may have allergies to iodinated contrasts, patients may also have allergic reactions to MRI or gadolinium-based contrasts. While gadolinium contrast allergies are quite rare, when they do occur, they can result in serious conditions, such as nephrogenic systemic fibrosis, depending on the contrast agent used. For this reason, Dr. Ruff emphasizes the importance of placing more attention on provider and patient awareness of the specific contrast agent.
[Dr. Christopher Beck]:
So let me take a little bit of a left-hand turn and instead of talking about iodinated contrast, we talk about some MRI or gadolinium-based contrast agents, so specifically not as much with allergic reactions, although I think that you can have an allergic reaction to MRI contrast agents. Can you speak a little bit about how often this occurs?
[Dr. Cullen Ruff]:
It is less common. The literature, again, a source like the ACR’s Manual on Contrast Media can be specific with regard to larger studies. I know that in our study where we had a cohort of over 300 patients with an iodinated contrast allergy, only four people we had to exclude because they actually were not allergic to an iodine-based contrast but claimed to be allergic to a gadolinium-based contrast. But what we did notice was not one of them specified Gadavist, Magnevist, Eovist, or whatever. The best they could say was gadolinium, and we know from the research that knowing which gadolinium-based MRI agent people have had is important, because some of these agents are more prone or less likely to cause conditions kind of like nephrogenic systemic fibrosis. So we started out using MRI contrast with impunity, not worrying about renal failure, et cetera, then realized that there are a few patients that are actually showing this condition. It's not common, but it's serious when it happens. And now that people have paid a little more attention to which agents cause it, it allows us to avoid having that, and maybe again, start injecting with impunity as long as we use agents that don't cause this condition.
[Dr. Christopher Beck]:
So that's a little bit telling of how long you've been out in practice Cullen, that you were part of the age when if someone was allergic or had allergic contrast or had renal insufficiency that you guys would just do contrasted studies with MRI.
[Dr. Cullen Ruff]:
That's absolutely right. We didn't care what their renal function was until we learned the hard way that it was important for some patients receiving some contrasts agents.
[Dr. Christopher Beck]:
All right. And predictably, now the pendulum is starting to swing back and that, NSF, so certainly serious, uncommon, but when it does happen, it can be quite debilitating.
Podcast Contributors
Dr. Cullen Ruff
Dr. Cullen Ruff is a practicing diagnostic radiologist and associate professor in Virginia.
Dr. Christopher Beck
Dr. Chris Beck is a practicing interventional radiologist with Regional Radiology Group in New Orleans.
Cite This Podcast
BackTable, LLC (Producer). (2021, November 26). Ep. 168 – Debunking Contrast Allergies [Audio podcast]. Retrieved from https://www.backtable.com
Disclaimer: The Materials available on BackTable.com are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
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