CHOOSING WISELYVR : THINGS WE DO FOR NO REASON Avoiding Contrast-Enhanced Computed Tomography Scans in Patients With Shellfish Allergies Anand K. Narayan, MD, PhD1*, Daniel J. Durand, MD1, Leonard S. Feldman, MD2 1Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; 2Department of Medicine and Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland. The “Things We Do for No Reason” (TWDFNR) series presenting to a pediatrics clinic with a suspected sea- reviews practices which have become common parts of food or shellfish allergy cited iodine as the culprit.2 hospital care but which may provide little value to our As contrast-enhanced CT scans utilize a variety of patients. Practices reviewed in the TWDFNR series do iodine-based agents, patients are often told to avoid not represent “black and white” conclusions or clinical CT scans with iodinated contrast agents or receive practice standards, but are meant as a starting place for corticosteroid/antihistamine premedications prior to research and active discussions among hospitalists and undergoing CT scans to mitigate potentially life- patients. We invite you to be part of that discussion. threatening allergic reactions. A survey of radiolog- A 55-year-old patient with a history of chronic ists and interventional cardiologists revealed that obstructive pulmonary disease and diabetes mellitus 65.3% and 88.9%, respectively, asked about seafood presented to the emergency room with acute shortness or shellfish allergies prior to administering contrast of breath and right leg swelling that began 1 week after enhanced CT scans, and 34.7% and 50.0%, respec- lumbar disk surgery. The emergency department team tively, stated that they would withhold contrast decides against ordering a chest CT scan with contrast media or recommend premedication with corticoste- to evaluate for a possible pulmonary embolism after roid/antihistamines for patients with seafood or shell- noting that the patient’s allergies include shellfish, fish allergy.2 which cause urticaria and facial edema. A ventilation- perfusion scan reveals heterogeneous perfusion defects WHY ASKING ABOUT SHELLFISH ALLERGIES consistent with an intermediate probability (20%– BEFORE IV CONTRAST CT SCANS DOES NOT 80%) for pulmonary embolism. The treating physicians REDUCE THE RISK OF CONTRAST consider starting the patient on a steroid regimen to pre- REACTIONS pare him for a CT scan with IV contrast, while pre- What Causes Allergic-Like Reactions to Fish and sumptively anticoagulating the patient for 24 hours in Shellfish? order for the steroids to provide maximal protective Allergic reactions are inappropriate or exaggerated effect before obtaining the scan. Should a history of immune response (hypersensitivity reaction). Four types shellfish allergy affect decision making regarding of hypersensitivity reactions have been described (type whether to administer IV contrast? I–IV)3; allergic reactions mediated by immunoglobulin E (IgE) represent type I hypersensitivity reactions. WHY YOU MIGHT THINK ASKING ABOUT Although fish and shellfish contain iodine, so too do SHELLFISH ALLERGIES BEFORE a wide variety of commonly consumed foods (eg, PERFORMING CONTRAST-ENHANCED CT yogurt, milk, bread). In addition, our bodies contain SCANS IS HELPFUL and require sufficient quantities of iodine for basic Fish and shellfish contain iodine, and allergic reac- functions, making immune reactions to such an essen- tions to seafood are quite common, with a prevalence tial ingredient of life unlikely. Instead, fish and shell- ranging anywhere between 2% and 6% of the popu- fish contain proteins (parvalbumin and tropomyosins, lation.1 As a result, patients with suspected shellfish respectively), which act as the major allergens, not allergies are often told by providers that they are iodine.4 allergic to iodine. In 1 study, nearly 92% of patients What Causes Reactions to IV Contrast Media? Around the world, tens of millions of injections occur *Address for correspondence and reprint requests: Anand Narayan, MD, every year for contrast-enhanced scans.5 Reactions to Department of Radiology, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Baltimore, MD 21287; Telephone: 410-955-6500; IV contrast media are not uncommon, occurring any- Fax: 410-550-1183; E-mail: [email protected] where between 0.6% and 17% of the time, with Additional Supporting Information may be found in the online version of severe reactions occurring between 0.02% and 0.5% this article. of the time.6 Higher reaction rates were associated Received: July 28, 2015; Revised: October 5, 2015; Accepted: October with the use of higher-osmolarity contrast agents. A 7, 2015 2015 Society of Hospital Medicine DOI 10.1002/jhm.2509 review of research studies found a lower rate of reac- Published online in Wiley Online Library (Wileyonlinelibrary.com). tions to IV contrast in eras in which low-osmolarity An Official Publication of the Society of Hospital Medicine Journal of Hospital Medicine Vol 11 | No 6 | June 2016 435 Narayan et al | Shellfish Allergies and CT Scans agents were exclusively used (0.2% after 1991) versus of the results found no statistically significant differen- eras in which high-osmolarity agents were exclusively ces comparing the frequencies of contrast reactions in used (7.0% between 1985 and 1986).7 patients with seafood allergy (15.0%) compared with Reactions to contrast include allergic-like reactions as other allergens (eggs, milk and chocolate, 14.6%; gen- well as a variety of other reactions (eg, arrhythmias, vas- eral allergies, 13.1%; fruit allergies, 12.9%; asthma, ovagal reactions, flushing), which are thought to be 11.2%; P values ranging between 0.2 and 0.6).6 Over- related to the dose and concentration of contrast media.8 all, the results suggest that patients with seafood Allergic-like, or anaphylactoid, reactions related to allergy are at no higher risk for having a contrast contrast are largely thought to have a fundamentally reaction compared with patients with other food aller- different molecular mechanism than true classic aller- gies or other forms of atopy. gic reactions. Anaphylactoid reactions are caused by Additionally, seafood and other food allergies direct release of histamine into the bloodstream in should be distinguished from food intolerances in response to interacting with chemicals. These reac- which the ingestion of histamine-rich materials in con- tions are not related to or mediated by IgE antibodies junction with histamine inhibitors (drugs or alcohol) and do not require prior exposure. leads to symptoms that can mimic allergic-like reac- True classic allergic reactions, on the other hand, tions (urticaria, pruritus, diarrhea, asthma).12 are mediated by IgE antibodies in which initial expo- sure to an allergen (antigen) is followed by subsequent What Do the Guidelines Recommend? 9 exposure and production of IgE antibodies. The aller- For patients who require IV contrast media for CT gen–IgE antibody complex causes the degranulation of scans, the American Academy of Allergy, Asthma, and mast cells and basophils, leading to the release of Immunology recommends not routinely ordering low– histamines. iso-osmolar radiocontrast media or pretreating with Reactions to IV contrast are likely related to some corticosteroids and antihistamines for patients with a component of the contrast media instead of the iodine 13 history of seafood allergy. The American College of itself. It is thought that the majority of these reactions Radiology recommends pretreatment with corticoste- are anaphylactoid reactions instead of true classic roids only for those patients who have previously expe- allergic reactions, given that IgE antibodies are not rienced moderate to severe reactions to IV contrast.8 consistently elevated in patients who exhibit these 8 reactions. Nevertheless, the symptoms of these 2 WHAT YOU SHOULD DO INSTEAD: ASK types of reactions (anaphylactoid and allergic reac- ABOUT PRIOR CONTRAST REACTIONS tions) are similar and require comparable treatment to BEFORE ADMINISTERING CONTRAST prevent life-threatening anaphylaxis. When a patient presents for a contrast-enhanced CT What Are the Major Risk Factors for Allergic-Like scan, patients should be asked if they have experi- Contrast Reactions? enced reactions to contrast and the severity and type Previous studies on risk factors for allergic-like con- of the associated reactions. Providers and support staff trast reactions suggest that the strongest predictor of should not ask specifically about shellfish allergies, as future contrast reactions is a history of prior contrast they have not been found to be associated with an ele- reaction (5-fold higher risk), with an estimated 10% vated risk of contrast reactions compared with other to 35% recurrence risk of contrast reactions.8 Patients allergens. Although all allergies seem to increase the with a history of atopy, asthma, and food allergies likelihood of having a reaction to contrast, only a his- (including seafood) are at approximately 2 to 3 times tory of previous contrast reactions will prompt a greater risk of contrast reactions.9 change in management. Asking specifically about sea- food allergies before performing an IV contrast CT Do Shellfish Allergies Place Patients at Higher Risk scan is a Thing We Do for No Reason. for Contrast Reactions Than Other Allergies? In 1 of the few studies evaluating seafood allergies RECOMMENDATIONS specifically, Witten et al. compared the frequency of contrast reactions in patients with histories of seafood 1. Before performing contrast-enhanced CT scans, allergy, food allergy, asthma, hay fever, hives, and patients should be asked if they have experienced contrast medium.10 Using their results, we compared reactions to IV contrast. There is no reason for pro- the frequency of reactions in patients with histories of viders and support staff to specifically inquire about seafood allergy (6.3%, 4/64) to patients with any seafood allergies. other type of allergy or atopic state (9.2%, 212/2304) 2. Patients with seafood and other food allergies do not and found no statistically significant differences (P 5 require premedication prior to CT scans.