Allergy to Contrast Media

Introduction

Contrast allergy is an immunologic and clinical reaction appearing hours to days after administration of iodinated or gadolinium-based contrast media.

  • Iodinated contrast used in computed tomography (CT), angiography, urography
  • Gadolinium-based contrast agents (GBCAs) used in magnetic resonance imaging (MRI)



Risk Factors

Allergic-like reactions to modern iodinated and gadolinium-based contrast media are uncommon.

  • Iodinated: 0.6% aggregate, 0.04% severe.
  • Gadolinium-based: 0.01-0.22% aggregate, 0.008% severe.
Risk factors exist that increase the allergic risk of a contrast reaction, include
  • Patients who have had a prior allergic-like reaction or unknown-type reaction 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.
    • In general, patients with unrelated allergies are at a 2- to 3-fold increased risk of an allergic-like contrast reaction, but due to the modest increased risk, restricting contrast medium use or premedicating solely on the basis of unrelated allergies is not recommended.
    • 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).
    • There is no cross-reactivity between different classes of contrast medium. For example, a prior reaction to gadolinium-based contrast medium does not predict a future reaction to iodinated contrast medium, or vice versa, more than any other unrelated allergy
  • A history of asthma increases the likelihood of an allergic-like contrast reaction.
    • Due to the modest increased risk, restricting contrast medium use or premedicating solely on the basis of a history of asthma is not recommended.
  • There is some evidence that contrast reactions are more common in anxious patients.



Corticosteroid Premedication

Given that premedication does not prevent all reactions, has not been confirmed to reduce the incidence of moderate or severe reactions or reaction-related deaths, has limited supporting efficacy in high-risk patients, and is accompanied by direct and indirect harms, the utility of premedication in high-risk patients is uncertain.

According to ACR Manual on Contrast Media 2023,

  • Premedication may be considered in patients with a prior allergic-like or unknown-type contrast reaction to the same class of contrast medium (e.g., iodinated - iodinated) and the use of premedication is not anticipated to adversely delay care decisions or treatment.
  • Regardless of patient status, history of a prior severe contrast reaction is considered a relative contraindication to receiving the same class of contrast medium in the future.
  • Routine premedication or avoidance of contrast medium for other indications, such as allergic reactions to other substances (including shellfish or contrast media from another class [e.g., gadolinium-based - iodinated]), asthma, seasonal allergies, or multiple drug and food allergies is not recommended.

NOTE: A randomized trial showed that premedication of average-risk patients prior to high- osmolality iodinated contrast medium administration reduces the likelihood of immediate adverse events of all severity. However, high-osmolality contrast medium is no longer used for intravascular purposes.



Recommended Premedication Regimens

Premedication Regimens for Allergy to Contrast Media

NOTE: Reactions can still occur despite premedication (a breakthrough reaction) and typically manifest with similar symptoms and severity as the patient's previous reaction. As a result, the benefit and risk of the imaging procedure should be carefully considered in patients with a history of a severe life-threatening allergic-like reaction.



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