| Contrast Allergy
Ashley Davidoff MD
CLINICAL CONSIDERATIONS About 2% of patients have a mild allergy to contrast manifesting with hives or mild swelling or itchiness of the thoat. Less than 1% have reaction to gadolinium. 1 in 1000 have a severe reaction and 1 in 250,00 die from the contrast. There is no increased risk of allergic reation to those patients with shell fish allergy and iodine allergy. Some patients are sensitive to the contrast but are not allergic. Contrast can induce a feeling of warmth, flushing, or nausea, and some patients may vomit. In this instance the presentation is not related to an allergic reaction and rather is a sensitivity. It is important to inform the patient of this distinction so that they do not get labelled as “allergic to contrast” Severity of reactions A minor reaction includes urticaria, pruritus and diaphoresis.. A moderate reaction includes facial swelling, throat tightness, bronchospasm, and a severe reaction includes seizures, pulmonary edema pulmonary arrest, cardiac arrest. Contrast Agents Non -ionic contrast The non ionic contrasts have reduced the incidence of reactions by about 5 fold but have not reduced the mortality rate. Oral contrasts Oral contrasts do not usually get absorbed, and so a patient who has had previous reaction to i/v contrast usually will be given the oral contrast . In the instance where the patient has a mucosal breech (IBD severe colitis, ulcer disease) contrast can become systemic. A barium based oral contrast agent (rather than an iodine based contrast) is indicated in this instance. IMAGING STRATEGIES The clinician and radiologist have to decide whether there is risk, and what sort of risk the patient is subjected to undergoing the test. In a patient who has truly had a mild or moderate reaction (hives or swelling) premedication will reduce this incidence by about 5-10%. In a patient with previous severe reaction an alternate study should be consisdered WHAT STUDY? For those patients having had a severe reaction an MRI with or without gadolinium or a CT study without i/v contrast or an ultrasound are the considerations depending on the clinical question. WHY? CT without contrast or US may be able to answrer the clinical question. MRI – The reaction to gadolinium and iodine are not related.
BACKGROUND TO THE DISEASE: 2% of patients getting iodinated contrast media and fewer than 1% of patients getting gadolinium contrast media will develop a mild reaction. (skin hives or minimal The five basic types of contrast reactions are: Skin hives: may take several days to go away. Throat tightening or laryngeal edema: -often accompanied by swelling of the face. Asthma: Asthmatics are more prone to this reaction. Shock: . This is a medical emergency Delayed: Some patients experience headaches, muscle pains and flu-like symptoms up to 48 hours after contrast media. This is a self limited reaction. HOW TO ORDER? If the patient has had a previous reaction to contrast it is usually the responsibility of the ordering physician to order the premedication in advance of the study since the protocol requires the patient to start pretreatmnet 24 hours before the study. The written order should include a statement about allergies, prior contrast reaction, detail of the reaction, and any history of gastrointestinal disease. PREPARING THE PATIENT Premedication Prednisone 50mg 24h,12h and 1h before scan with 50mg of benadryl 1h for non emergent cases. For patients who can not take po., we use Solumedrol 40mg 24h,12, and 1h before scan with 50mg IV benadryl on call before the scan. Use non-ionic contrast agents.
When there is an emergent situation and i/v contrast is needed then; Hydrocortisone i/v 200mg every 4 hours till the procedure and 50mg Benadryl i/v on call or one hour before the procedure
CLINICAL RED FLAGS: Risk factors include a previous reaction, allergic history requiring medication, asthma. Pretesting is a poor predictor of future reactions.
References: Aspelin P, Stacul F, Thomsen et al Effects of iodinated contrast media on blood and endothelium. Eur Radiol. 2006 Jan 5;:1-9 (Related Articles, Links)
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