Seafood Myth
Seafood Allergy and Radiocontrast Media: Are Physicians Propagating a Myth?
Andrew D. Beaty, Philip L. Lieberman, Raymond G. Slavin
The American Journal of Medicine (http://www.amjmed.com/article/PIIS000293430700842X/fulltext#fig1) - February 2008 (Vol. 121, Issue 2, Pages 158.e1-158.e4, DOI: 10.1016/j.amjmed.2007.08.025)
BACKGROUND
More than 10 million procedures using radiocontrast media are performed every year. Various studies have reported the rate of adverse events from radiocontrast media administration at 5% to 12% for high-osmolality contrast media and 1% to 4% for low-osmolality contrast media.1, 2, 3, 4 Severe, life-threatening reactions are relatively rare, with 1 large retrospective study reporting rates of 0.22% and 0.04% with high and low-osmolality contrast media, respectively.5
Immediate-type adverse reactions to radiocontrast media are virtually always non-immunoglobulin (Ig)-E mediated and have thus been previously termed “anaphylactoid reactions.” It was recently recommended that the term “nonimmunologic anaphylaxis” be used to describe these types of reactions.6 Like true IgE-mediated anaphylactic reactions, they typically occur within 1 hour of exposure and can manifest as hives, angioedema, respiratory compromise, and cardiovascular collapse. Various potential pathogenic mechanisms have been investigated, including the direct induction of histamine release, complement activation, and recruitment of various mediators.7 However, the true cause has not been elucidated.
Nonimmunologic anaphylactic reactions to radiocontrast media have been the subject of numerous publications in the medical literature during the past 30 years. Many of these publications have examined allergies as risk factors for adverse reactions to radiocontrast media, and it is now well accepted that allergic individuals in general are at a mildly increased risk for developing adverse reactions to radiocontrast media.5, 8
It has been well established that patients with true allergy to seafood and shellfish have specific IgE against proteins within the meat of the fish, and that iodine content plays no etiologic role. Because severe radiocontrast media reactions are almost always non-IgE mediated, the idea of cross-reactivity between iodine and radiocontrast media has been effectively discounted.
Despite the increase in understanding both seafood allergy and the nature of radiocontrast media reactions, we hypothesized that seafood allergy is still considered to be a more significant risk factor for anaphylactoid reactions to radiocontrast media than other food allergies. One possible explanation for this continued misconception is that the physicians directly responsible for the actual administration of radiocontrast, namely, radiologists and interventional cardiologists, are in fact contributing to its propagation.
METHODS
An anonymous, informal, 8-question yes/no survey was designed (Figure 1). Two of the questions (Figure 1; Questions 3 and 6) dealt directly with seafood allergy, and the remaining 6 questions were intended as distracters to obscure the survey’s true intent. The survey was sent to 231 faculty radiologists and interventional cardiologists at 6 Midwestern academic medical centers. Included with each survey was a brief cover letter explaining that the survey was intended to assess how physicians administer radiocontrast screen for the possibility of adverse events. The wording of 1 distracter question was modified slightly to allow the subdivision of responses among radiologists and cardiologists.

RESULTS
Of the 231 physicians surveyed, 113 (48.9%) responded. To the first question related to seafood (Figure 1; Question 3), 65.3% of the radiologists and 88.9% of the cardiologists replied in the affirmative. To the second question related to seafood (Figure 1; Question 6), 34.7% of the radiologists and 50% of the cardiologists responded “yes.”
RESULTS
A misconception about seafood allergy and its relation to radiocontrast media reactions continues to be pervasive among both the medical community and the public at large. The precise origins of the misconception are not entirely known, but the basic notion itself can be traced back more than 30 years. A landmark retrospective study by Shehadi9 in 1975 evaluated patients with previous adverse reactions to radiocontrast. Among these patients, 14.98% reported a personal history of shellfish allergy, although there was no objective confirmation of allergy. She had surmised that iodine contained within the seafood and shellfish cross-reacted with iodine contained in the radiocontrast, thus predisposing seafood-allergic patients to radiocontrast reactions. Of note, nearly identical numbers of patients reported allergies to other foods, such as milk and egg, in the same study.
A 2005 survey of 75 patients with seafood allergy confirmed by skin testing and radioallergosorbent testing revealed that 65% of responders had either read or been told that they should avoid iodine-containing radiocontrast because of their allergy. Moreover, 92% of responders thought that iodine in seafood was responsible for their allergic reaction.10 However, these misconceptions clearly go beyond the general public, as demonstrated in a 2004 survey of 157 physicians at an academic medical center in Israel. Among the responders, a majority indicated that they would advise a patient who had a history of nonimmunologic anaphylactic reaction to radiocontrast to avoid future ingestion of fish and other seafood. A significant majority also indicated that they would have such patients avoid or reduce the use of iodine-containing solutions.11
Our survey was certainly not without limitations. It was informal and thus not standardized. It also did not differentiate between low-osmolarity contrast media and high-osmolarity contrast media for the sake of brevity, although many medical centers today use low-osmolality contrast exclusively. Despite these minor limitations, some interesting observations can be made from the results. First, more than one third of all responders replied that they would either withhold radiocontrast media or premedicate on the basis of a history of seafood allergy. This indicates that even among faculty physicians at academic medical centers, who are on the cutting edge of their respective fields, this misconception remains fairly pervasive. Furthermore, this survey was limited to those directly responsible for radiocontrast administration and who presumably have the most direct knowledge about radiocontrast.
Another interesting, and possibly even more telling, observation from this survey is that approximately two thirds of the responders answered that they inquire about a history of seafood allergy before giving radiocontrast media. Thus, although only approximately one third of the physicians indicated that they would change their management before radiocontrast administration on the basis of a history of seafood allergy, approximately twice that many inquire about such a history. This begs a question for the approximately one third who ask about the history but would apparently not alter their management given a positive response. What is the purpose of asking the question if no action will be taken based on the answer?
It seems possible that the very act of inquiring about a history of seafood allergy before the administration of radiocontrast itself could contribute to propagating the misconception that a positive history confers significant risk. Regardless of whether it alters clinical practice, questioning a patient about a history of seafood allergy before the administration of radiocontrast could certainly lead that patient to presume that there is an inherent risk in one who is seafood allergic. This effect also is likely to occur among medical trainees and others who observe these questions being asked, unless they are specifically told that the answer will not affect treatment.
CONCLUSIONS
The misconception of seafood allergy as a significantly greater risk factor for adverse reactions to radiocontrast is among the most well publicized in the medical literature. Our informal survey demonstrates that even among highly trained academic faculty physicians who frequently administer radiocontrast, the myth persists. This has occurred despite significant advances in our understanding of both seafood allergy and nonimmunologic anaphylactoid reactions to radiocontrast. Although only approximately one third of responders replied that they would alter their course of action regarding radiocontrast administration based on seafood allergy, the fact that more than two thirds continue to ask about it is telling. The questioning itself likely plays a considerable role in the persistence of this notion, because in addition to patients, medical students, residents, and fellows are presumably in attendance when the faculty member poses the question.
A recent survey by the Food Allergy and Anaphylaxis Network estimated the prevalence of seafood allergy in the United States at approximately 2.3%, which translates to approximately 6.6 million Americans. Thus, a substantial portion of the American public stands to be affected by the continued propagation of this misconception and could potentially have standard-of-care procedures deferred or unnecessary medications administered on the basis of their allergic history. If the antiquated practice of inquiring specifically about seafood allergy history before radiocontrast administration could finally be put to rest, particularly at academic medical institutions where the practice may be observed by trainees, this myth would likely take its rightful place in oblivion. There is clearly a vital need for continuing education of physicians with respect to seafood allergy and radiocontrast administration.
References
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