A previous reaction to seafood, povidone iodine, or other iodine-containing substance does not have any predictive value beyond a reaction to contrast material. The practitioner may also counsel the patients who have had a reaction to contrast material that they can continue to ingest iodine-containing foods or drugs. The false link between iodine-containing foods and contrast material can be traced to two studies in the early 1970s that reported a 6% rate of reaction in patients with a reported seafood allergy. Subsequent reports have not confirmed these findings. Instead, oversight committees, such as the one sponsored by the American College of Radiology, have regularly counseled that a seafood allergy should be considered in the same category as any other allergy when considering the individual risk of contrast material to the patient. Unfortunately, reports firmly establish that physicians resist performing needed studies in patients with a seafood allergy. In 2004, Confino-Cohen and Goldberg reported that 77% of physicians would have unnecessarily withheld radiocontrast material in patients with a history of a seafood allergy or rash after local application of iodine-containing antiseptics. Moreover, 69% of them would have taken various irrelevant precautions when using iodine-containing antiseptics in patients who have had a history of reaction to an iodinated contrast media (ICM).

ICM is regularly used for opacification in computed tomography, excretory urographic, and angiographic studies. ICM is classified into two groups: ionic high-osmolality contrast media and nonionic low-osmolality contrast material. The former is associated with a 5% to 12% incidence of adverse reactions, whereas the latter is associated with a 1% to 3% incidence, but because they both contain iodine, the discrepancy is related to another property of the media.