PROVE IT
Even doctors believe myth
January 30, 2010
THE CLAIM
If you have a seafood allergy, avoid CT scans.
THE FACTS
Seafood allergies represent the most common form of food allergies in adults, affecting about 2 per cent to 3 per cent of Americans. But myths about the condition abound.
The most prevalent falsehood may be that allergies to shellfish in particular, which account for most seafood allergies, are caused by an intolerance to their iodine content. As a result, many patients who show up at hospitals for CT scans and other X-ray imaging procedures that involve ingesting iodine-containing contrast agents worry about severe allergic reactions.
According to studies, the notion is a myth: The allergies are caused by proteins in the animals, not their iodine content. But researchers have found that the myth persists at least in part because doctors help propagate it.
One study said the belief was so prevalent that about 70 per cent of radiologists and cardiologists who were surveyed said they regularly asked patients whether they had seafood allergies before administering radiocontrast agents before procedures, and 40 per cent said they would not administer them to patients who answered yes.
In reality, the general risk of an adverse reaction to a contrast agent ranges from 0.2 per cent to 17 per cent (depending on several factors), with severe reactions extremely rare. But studies show that an allergy of any kind, be it asthma or an allergy to shellfish or another food, raises the risk by the same amount. Ultimately, no more than 15 per cent of patients with seafood allergies experience reactions.
THE BOTTOM LINE
Seafood allergies are not caused by iodine.
The New York Times
Toronto Star
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