Computed Tomography (CT) scan using radiocontrast is one of the most common imaging modalities used in emergency departments today. Several studies and my own anecdotal experiences indicate that both physicians and patients believe that iodine allergies are linked to seafood allergies, and that both are related to a disproportionate increased risk of “allergic” reactions to radiocontrast agents. But is iodine allergy fact or fiction?
Is “iodine allergy” real – or just a medical myth?
Computed Tomography (CT) scan using radiocontrast is one of the most common imaging modalities used in emergency departments today. Several studies and my own anecdotal experiences indicate that both physicians and patients believe that iodine allergies are linked to seafood allergies, and that both are related to a disproportionate increased risk of “allergic” reactions to radiocontrast agents.
But is iodine allergy fact or fiction? As it turns out, iodine is found throughout our bodies in thyroid hormones and amino acids, and it is even added to most salt used in the United States to prevent iodine deficiency. A person simply cannot survive without iodine. While it is true that fish and shellfish both contain iodine, the major allergens are tropomyosins and parvalbumin, respectively [4]. Iodine simply is not an allergen.
Table 1: What is the evidence for risk factors for radiocontrast allergy to low-osmolar contrast agents [2, 5]?
TABLE 1 BOTTOM LINE: As the chart indicates, there is an increased risk of radiocontrast allergy in patients with any type of allergy, atopy, and/or prior contrast reactions, compared to the general population, with low-osmolar contrast media, but it is significantly less than high-osmolar contrast media. There were zero deaths.
Table 2: What is the evidence for pretreatment with steroids to prevent contrast allergy [3]?
TABLE 2 BOTTOM LINE: As indicated in the chart, steroid pre- medication has not been shown to decrease the rate of severe reactions (i.e. immediately life-threatening or requiring hospitalization), but has been shown to reduce mild reactions.
In Brief
1. Seafood allergy confers the same risk of radiocontrast reaction as:
• Any allergies (Not just seafood allergies);
• Having previous reaction to a contrast agent; and
• Evidence of atopy, i.e., asthma.
2. Iodine is NOT an allergen.
3. Low Osmolar Contrast agents have significantly reduced the number of severe reactions to radiocontrast.
4. Premedication with steroids has not been shown to decrease the number of severe allergic reactions to radiocontrast.
REFERENCES
1. Beaty, Andrew D, Philip L Lieberman, and Raymond G Slavin. 2008. Seafood allergy and radiocontrast media: are physicians propagating a myth? The American journal of medicine, no. 2. doi:10.1016/j.am- jmed.2007.08.025. http://www.ncbi.nlm.nih.gov/pubmed/18261505.
2. Kopp AF et al. Prevalence of Acute Reactions to Iopromide: Postmarketing Survelillance Study of 74,717 Patients. Acta Radio 2008; 49 (8): 902 -11. http://www.ncbi.nlm.nih.gov/pubmed/18651252.
3. Lasser, E C, C C Berry, L B Talner, L C Santini, E K Lang, F H Gerber, and H O Stolberg. 1987. Pretreatment with corticosteroids to alleviate reactions to intravenous contrast material. The New England journal of medi- cine, no. 14 ( 1). http://www.ncbi.nlm.nih.gov/pubmed/3627208.
4. Schabelman, Esteban, and Michael Witting. 2010. The relationship of radiocontrast, iodine, and seafood allergies: a medical myth exposed. The Journal of emergency medicine, no. 5 (January 4). doi:10.1016/j. jemermed.2009.10.014. http://www.ncbi.nlm. nih.gov/pubmed/20045605.
5. Valls C et al. Selective Use of Low-Osmolality Contrast Media in Computed Tomography. Eur Radiol 2003; 13 (8): 2000-5. http://www.ncbi.nlm.nih.gov/pubmed/12942301.