What is the recommended protocol for administering contrast agents to patients with a known iodine allergy?

From the Guidelines

Patients with a known iodine allergy do not have a significantly increased risk of reaction to contrast agents, as the term "iodine allergy" is a misnomer and reactions to contrast media are not related to iodine 1. The concept of an "iodine allergy" is often misunderstood, and it's essential to recognize that reactions to contrast media are not mediated by iodine.

• The incidence of anaphylactoid reactions to contrast media is approximately 1% 1.
• The use of premedication in patients with prior contrast reactions is a topic of debate, with some studies suggesting that it may not be beneficial in preventing anaphylaxis 1.
• However, in clinical practice, premedication is often used to reduce the risk of recurrent anaphylactoid reactions, especially in patients with a history of severe reactions.
• A standard premedication regimen may include prednisone and diphenhydramine, but the effectiveness of this approach is not universally agreed upon, and the decision to use premedication should be made on a case-by-case basis, considering the individual patient's risk factors and medical history.
• It's also important to note that low-osmolality or iso-osmolality contrast agents are preferred over high-osmolality agents, as they are less likely to cause adverse reactions 1.
• Ultimately, the management of patients with a known "iodine allergy" who require contrast agents should be individualized, taking into account the patient's specific medical history, the severity of any previous reactions, and the potential benefits and risks of premedication and contrast agent administration.

From the Research

Iodine Allergy and Contrast Reaction

• The prevalence of allergic reactions to iodinated contrast media (ICM) is estimated to be 1:170,000, which is approximately 0.05%-0.1% of patients undergoing radiologic studies with ICM 2.
• The risk factors for immediate reactions include poorly controlled bronchial asthma, concomitant medication, rapid administration of the ICM, mastocytosis, autoimmune diseases, and viral infections 2.
• Hypersensitivity reactions can appear within the first hour after administration (immediate reactions) or from more than 1 hour to several days after administration (nonimmediate or delayed reactions) 2.

Recommended Protocol for Administering Contrast Agents

• Premedication with cetirizine and prednisone before radiologic procedures proved to be efficient in patients with a history suggesting hypersensitivity to iodinated contrast media 3.
• Using an iodinated contrast material (ICM) substitution was more effective for preventing repeat allergic-like reactions than using steroid premedication and the same ICM that caused the previous reaction 4.
• Collaboration between the prescribing physician, the radiologist, and the allergist, and an accurate allergologic workup are essential to ensure maximum safety for the patient 5.

Diagnostic Approach to Hypersensitivity Reactions

• Skin tests and drug provocation tests (DPT) with ICM are used to diagnose hypersensitivity reactions to iodinated contrast media 5.
• The skin test showed a very high negative predictive value (NPV) compared to DPT in patients with a previous immediate adverse reaction 5.
• The NPV of the allergologic workup protocol was elevated (92.3%) for patients undergoing DPT and subsequent exposure to the same ICM in a real-life setting 5.

Prevention of Allergic-like Reactions

• Premedication with antihistamines and corticosteroids is still widely used, but evidence of its efficacy is lacking and there is a risk for under-estimation of possible severe adverse reactions to ICM in those who undergo premedication 6, 5.
• The mechanism of CM-induced allergy-like reaction remains disputed, with relatively recent data reviving the hypothesis of a type-I hypersensitivity mechanism 6.