I am suddenly VERY allergic to shrimp. Huh.
Bummer... Be careful around other shellfish as well. You probably guessed that already.
Yeah, shrimp is my big favorite, but oh, well.
Oh that sucks. My wife also has this problem and the downstream related problems so... sorry about your new iodine contrast allergy. Sort of.
Most of the scientific and medical literature says that there is no relationship between having a shellfish allergy and an allergy to iodine contrast dyes, however if you mention that you have a shellfish allergy, radiologists will assume you are allergic to the normal iodine dye and refuse to use it on you.
Yikes. I had no idea.
@celticcanon has it correct. It’s another medical myth that’s persisted despite clear data since its origin in the 70s. And radiologists still get it wrong even today. Imagine that.
Why it is not true
• Shellfish allergy is to proteins, not iodine. The main allergen is tropomyosin (a muscle protein), sometimes with other proteins. Iodine content in shellfish is irrelevant to the allergic response. 
• Iodine itself is not an allergen. It is an essential element the body uses (e.g., for thyroid hormones) and is present in iodized salt. There are no documented true IgE-mediated allergic reactions to elemental iodine. Reactions sometimes blamed on “iodine” (such as to povidone-iodine skin prep) are usually due to other components in the product. 
• Contrast reactions work differently. Most immediate reactions to iodinated contrast media are anaphylactoid (non-IgE-mediated). They are thought to involve direct mast-cell/basophil activation related to the agent’s physicochemical properties (especially hyperosmolarity in older high-osmolar agents), not an immune response to iodine. Modern low- or iso-osmolar non-ionic contrast agents have lower reaction rates
The interesting thing is that this myth doesn't just persist with radiologists, but with experienced doctors as well. When my daughter had her last round of imaging, I asked the radiologist (not the tech, the actual doctor) about iodine allergies and he told me that its not the iodine that causes the allergy, but proteins in dye that are still there because the iodine is extracted from shellfish. Which I could find no evidence of and doesn't really make sense. Even if the iodine in the dye was extracted from shrimp or whatever, the synthesis process would render it down to medically pure iodine.
All of which goes to show that no amount of education or professional standards can conquer the mythological side of the human brain.
