From the Guidelines
There is no significant cross-reactivity between CT contrast and MRI contrast in patients with a CT contrast allergy, as these agents have distinct chemical structures. The chemical composition of CT contrast agents, which are iodinated, differs from that of MRI contrast agents, which are gadolinium-based 1. This distinction is crucial in understanding the allergic potential of these agents. A study published in the journal Circulation in 2011 notes that the incidence of anaphylactoid reactions to contrast media is relatively low, at 1%, with severe reactions occurring in as low as 0.04% of cases 1. Key points to consider include:
- The lack of cross-reactivity between iodine in CT contrast and other allergies, such as seafood or shellfish allergies, as iodine does not mediate these reactions 1.
- Patients with a history of allergic reactions to one type of contrast agent may still be safely administered the other type, although precautionary measures like premedication with corticosteroids and antihistamines may be taken, especially in cases of severe previous reactions.
- The importance of patients informing their healthcare providers about any history of allergic reactions to contrast agents before undergoing imaging procedures. In clinical practice, the approach to patients with a history of CT contrast allergy who require MRI contrast involves considering the individual's specific allergy history and the potential benefits and risks of premedication protocols, as outlined in guidelines such as those reported in Circulation 1.
From the Research
Cross-Reactivity between CT and MRI Contrast
- There is limited evidence to suggest a direct cross-reactivity between CT contrast and MRI contrast in patients with a CT contrast allergy 2, 3, 4.
- A study published in 2019 found that gadobenate and gadobutrol, two types of MRI contrast agents, were associated with higher rates of allergic-like reactions compared to gadodiamide or gadoterate 2.
- Another study published in 2022 found that patients with systemic mastocytosis, a condition that increases the risk of hypersensitivity reactions, had a low risk of contrast media-induced hypersensitivity reactions, including those caused by CT and MRI contrast agents 3.
- A 2014 review article noted that hypersensitivity reactions to diagnostic contrast media and dyes are not common, but can occur, and that skin tests can be helpful in diagnosing patients with hypersensitivity reactions to these compounds 4.
Alternative Contrast Agents
- A 2005 study found that gadolinium, a contrast agent commonly used for MRI, can be used as an alternative to iodinated contrast media for X-ray angiography in patients with severe allergy to iodine or iodinated contrast agents 5.
- A 2013 review article discussed the use of premedication to prevent or reduce the occurrence of allergic reactions to iodinated contrast media in high-risk patients, and noted that identifying patients at high risk for an allergy-type reaction is an essential task of the radiologist 6.
Risk of Cross-Reactivity
- The available evidence suggests that the risk of cross-reactivity between CT and MRI contrast agents is low, but not negligible 2, 3, 4.
- Patients with a history of allergic reactions to CT contrast agents should be carefully evaluated and monitored before receiving MRI contrast agents, and vice versa 2, 3, 4.