USA.gov. In other words, allergic people can react to multiple different things! Even, those, who have an allergy to iodine cleaners that are used on the skin, may not be at risk of getting an allergy from iodine contrast.  |  Anaphylactoid reactions are caused by direct release of histamine into the bloodstream in response to interacting with chemicals. J Nucl Cardiol. doi: 10.1016/j.amjmed.2008.03.035. Among those patients who risk having an adverse reaction to contrast dye include patients with a history of asthma, cystic fibrosis, shellfish allergy, dehydration or constipation, habitual use of NSAIDs or beta blockers, heart disease, sickle cell, and renal disease. This review will discuss the relationship of radiocontrast, iodine, and seafood allergies. The urologist thought that the patient might have a renal mass and sent him to radiology for a CT scan. Although all allergies seem to increase the likelihood of having a reaction to contrast, only a history of previous contrast reactions will prompt a change in management. [8]WHAT YOU SHOULD DO INSTEAD: ASK ABOUT PRIOR CONTRAST REACTIONS BEFORE ADMINISTERING CONTRASTWhen a patient presents for a contrast‐enhanced CT scan, patients should be asked if they have experienced reactions to contrast and the severity and type of the associated reactions. Four types of hypersensitivity reactions have been described (type IIV)[3]; allergic reactions mediated by immunoglobulin E (IgE) represent type I hypersensitivity reactions. 2015 Jul 21;1:9. doi: 10.1186/s40942-015-0010-y. This site needs JavaScript to work properly. https://www.choosingwisely.org/. The method of entry of the contrast dye will vary based on the part of the body that is imaged. A 55‐year‐old patient with a history of chronic obstructive pulmonary disease and diabetes mellitus presented to the emergency room with acute shortness of breath and right leg swelling that began 1 week after lumbar disk surgery. National Center for Biotechnology Information, Unable to load your collection due to an error, Unable to load your delegates due to an error. This belief arises from “iodine allergies” because shellfish contain Iodine. Objectives: [12]What Do the Guidelines Recommend?For patients who require IV contrast media for CT scans, the American Academy of Allergy, Asthma, and Immunology recommends not routinely ordering lowiso‐osmolar radiocontrast media or pretreating with corticosteroids and antihistamines for patients with a history of seafood allergy. Up to 35% of patient will experience a recurrence if no premedication prophylaxis is given. [13] The American College of Radiology recommends pretreatment with corticosteroids only for those patients who have previously experienced moderate to severe reactions to IV contrast. Having a reaction to an iodine-based contrast dye is also not the same as an allergy to seafood, which may be rich in iodine. People who are allergic to scaled fish are typically allergic to a different muscle protein, parvalbumin. Results: [11] A reanalysis of the results found no statistically significant differences comparing the frequencies of contrast reactions in patients with seafood allergy (15.0%) compared with other allergens (eggs, milk and chocolate, 14.6%; general allergies, 13.1%; fruit allergies, 12.9%; asthma, 11.2%; P values ranging between 0.2 and 0.6). Copyright © 2010 Elsevier Inc. All rights reserved. Providers and support staff should not ask specifically about shellfish allergies, as they have not been found to be associated with an elevated risk of contrast reactions compared with other allergens. [8] Nevertheless, the symptoms of these 2 types of reactions (anaphylactoid and allergic reactions) are similar and require comparable treatment to prevent life‐threatening anaphylaxis. Challenges and opportunities in developing targeted molecular imaging to determine inner ear defects of sensorineural hearing loss. NIH A prior allergic-like reaction to intravascular iodinated contrast is the most substantial risk factor for a recurrent reaction upon future contrast administration. This causes the same reaction as the histamine release due to allergy. Severe allergy to iodine contrast and renal insufficiency are two main problems with iodine-based contrast media. HHS [8] Patients with a history of atopy, asthma, and food allergies (including seafood) are at approximately 2 to 3 times greater risk of contrast reactions. Allergies to shellfish, in particular, do not increase the risk of reaction to intravenous contrast any more that of other allergies. It may cause a rash in sensitive people. Severe reactions occur in 0.02-0.5% and deaths in 0.0006-0.006%; neither have been related to "iodine allergy," seafood allergy, or prior contrast reaction. CT Contrast Agents and Shellfish Allergies. This myth originated in the 1970s from a survey of patients who reported prior reactions to contrast media. A review of research studies found a lower rate of reactions to IV contrast in eras in which low‐osmolarity agents were exclusively used (0.2% after 1991) versus eras in which high‐osmolarity agents were exclusively used (7.0% between 1985 and 1986). Practices reviewed in the TWDFNR series do not represent black and white conclusions or clinical practice standards, but are meant as a starting place for research and active discussions among hospitalists and patients. Allergies to shellfish, in particular, do not increase the risk of reaction to intravenous contrast any more that of other allergies. Similarly, Shehadi evaluated seafood as well as asthma, hay fever, common medications (eg, penicillin, aspirin, morphine), and others. That fact aside, it is difficult to establish how the concern between seafood allergy and iodine first originated. [6] Overall, the results suggest that patients with seafood allergy are at no higher risk for having a contrast reaction compared with patients with other food allergies or other forms of atopy.Additionally, seafood and other food allergies should be distinguished from food intolerances in which the ingestion of histamine‐rich materials in conjunction with histamine inhibitors (drugs or alcohol) leads to symptoms that can mimic allergic‐like reactions (urticaria, pruritus, diarrhea, asthma). We invite you to be part of that discussion. eCollection 2015. We invite you to be part of that discussion. [7], Reactions to contrast include allergic‐like reactions as well as a variety of other reactions (eg, arrhythmias, vasovagal reactions, flushing), which are thought to be related to the dose and concentration of contrast media.[8]. The patient stated that he was not allergic to x-ray dye. [1] As a result, patients with suspected shellfish allergies are often told by providers that they are allergic to iodine. Four types of hypersensitivity reactions have been described (type IIV)[3]; allergic reactions mediated by immunoglobulin E (IgE) represent type I hypersensitivity reactions.Although fish and shellfish contain iodine, so too do a wide variety of commonly consumed foods (eg, yogurt, milk, bread). Shellfish and seaweed are the most common foods that contain high levels of iodine. Asking specifically about seafood allergies before performing an IV contrast CT scan is a Thing We Do for No Reason. Similarly, Shehadi evaluated seafood as well as asthma, hay fever, common medications (eg, penicillin, aspirin, morphine), and others. The major allergens in shellfish are tropomyosins, which are unrelated to iodine. [8]Allergic‐like, or anaphylactoid, reactions related to contrast are largely thought to have a fundamentally different molecular mechanism than true classic allergic reactions. [8] Nevertheless, the symptoms of these 2 types of reactions (anaphylactoid and allergic reactions) are similar and require comparable treatment to prevent life‐threatening anaphylaxis.What Are the Major Risk Factors for Allergic‐Like Contrast Reactions?Previous studies on risk factors for allergic‐like contrast reactions suggest that the strongest predictor of future contrast reactions is a history of prior contrast reaction (5‐fold higher risk), with an estimated 10% to 35% recurrence risk of contrast reactions. The treating physicians consider starting the patient on a steroid regimen to prepare him for a CT scan with IV contrast, while presumptively anticoagulating the patient for 24 hours in order for the steroids to provide maximal protective effect before obtaining the scan. [2]WHY ASKING ABOUT SHELLFISH ALLERGIES BEFORE IV CONTRAST CT SCANS DOES NOT REDUCE THE RISK OF CONTRAST REACTIONSWhat Causes Allergic‐Like Reactions to Fish and Shellfish?Allergic reactions are inappropriate or exaggerated immune response (hypersensitivity reaction). Contrast dye may be administered intravenously, orally or rectally. Patients with shellfish or povidone-iodine (e.g., Betadine®) allergies are at no greater risk from iodinated contrast medium than are patients with other allergies (i.e., neither is a significant risk factor) [5,6]. [8] Patients with a history of atopy, asthma, and food allergies (including seafood) are at approximately 2 to 3 times greater risk of contrast reactions.[9]. Method: The purported link between shellfish allergy and radiocontrast media is indeed mythical. Epub 2015 Mar 5. Ingested iodine is converted to iodide, the ionized form of iodine, in the gut. Westermann-Clark E, Pepper AN, Talreja N, Lockey RF. Should a history of shellfish allergy affect decision making regarding whether to administer IV contrast? A history of prior reaction to contrast increases the risk of mild reactions to as high as 7-17%, but has not been shown to increase the rate of severe reactions. You can be allergic to all types of shellfish or only to mollusks (clams, mussels, oysters and scallops as well as limpets, periwinkles, snails [escargot]… The following are some examples: Allergy: Patients who have had a prior allergic-like reaction or unknown-type reaction (i.e., a reaction of unknown manifestation) to contrast medium have an approximately 5-fold increased risk of developing a future allergic-like reaction if exposed to the same class of contrast medium again [3]. Soon after the injection, the patient went into anaphylactic shock on the CT table. In 1 study, nearly 92% of patients presenting to a pediatrics clinic with a suspected seafood or shellfish allergy cited iodine as the culprit. It is thought that the majority of these reactions are anaphylactoid reactions instead of true classic allergic reactions, given that IgE antibodies are not consistently elevated in patients who exhibit these reactions. The risk of reaction in patients with a seafood allergy is similar to that in patients with other food allergies or asthma. Radiocontrast agents are some of the most commonly used medications in the emergency department. 2008 Aug;121(8):e19. Here is a popular allergy myth: There are cross-reactions between seafood and iodinated contrast (x-ray contrast dye) caused by “Iodine allergy”. Gadolinium (Gd) has different chemical structure with no cross reactivity with iodine-based contrast media in patients with iodine allergy. Most people who are allergic to shellfish react to certain proteins these foods contain, not to iodine. [2] As contrast‐enhanced CT scans utilize a variety of iodine‐based agents, patients are often told to avoid CT scans with iodinated contrast agents or receive corticosteroid/antihistamine premedications prior to undergoing CT scans to mitigate potentially life‐threatening allergic reactions. Dietary sources include fish, iodized salt, and iodates used as bread preservatives. ... Shellfish allergy is an abnormal response by the body's immune system to proteins in certain marine animals. Instead, fish and shellfish contain proteins (parvalbumin and tropomyosins, respectively), which act as the major allergens, not iodine. [12], For patients who require IV contrast media for CT scans, the American Academy of Allergy, Asthma, and Immunology recommends not routinely ordering lowiso‐osmolar radiocontrast media or pretreating with corticosteroids and antihistamines for patients with a history of seafood allergy. A MRI with contrast dye is often performed on patients suspected of having cancer due to the level of detail that is available from the imaging. Iodine and Shellfish Allergy: A Myth that Lingers October 5, 2020 Close to 3% of the U.S. population is allergic to shellfish, according to the Journal of American Medical Association. Allergic‐like, or anaphylactoid, reactions related to contrast are largely thought to have a fundamentally different molecular mechanism than true classic allergic reactions. A survey of radiologists and interventional cardiologists revealed that 65.3% and 88.9%, respectively, asked about seafood or shellfish allergies prior to administering contrast enhanced CT scans, and 34.7% and 50.0%, respectively, stated that they would withhold contrast media or recommend premedication with corticosteroid/antihistamines for patients with seafood or shellfish allergy. 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