For decades there has been a misconception that patients with a shellfish allergy cannot receive certain imaging procedures with radiocontrast material, commonly referred to as contrast dye. This belief stems from the perceived link between shellfish allergies and adverse reactions to iodine. In this article, we break down one of the most persistent myths in modern medicine, how it came to be, and why it has since been disproved.
The myth started back in the 1970s based on a simple, but flawed, guess. Because both shellfish and medical contrast “dye” contain iodine, doctors assumed iodine was the culprit behind allergic reactions.
In reality, you actually can’t be allergic to iodine. It’s an element your body needs to survive and is present in most table salt. There have never been any reported IgE mediated (allergic) reactions to iodine.
Researchers have looked at tens of thousands of patients and found that being allergic to shellfish doesn’t mean you’ll have a problem with contrast. When people have a shellfish allergy, their immune system is actually attacking a protein in the meat called tropomyosin. Tropomyosin is a fish equivalent to human muscle protein and is not present in contrast dye.
The mechanism for allergic reactions to radiocontrast material is hyperosmolarity, a physiochemical property of the dye itself. Prior reactors to radiocontrast media should NOT be identified as having “iodine allergy”.
If your doctor orders a CT scan with contrast, don’t let a shellfish allergy scare you off. While you should always mention your allergies to the medical team, modern contrast is very safe. There is NO cause-and-effect connection between contrast media reactions and shellfish allergy.
