Severe Anaphylaxis From Iodinated Contrast Is Rare but Often Complex, Reveals Research
USA: A large study analyzing over 700,000 CT scans with iodinated contrast has reported a very low overall anaphylaxis incidence of 0.02%. However, among those who did develop anaphylaxis, 10% required multiple (≥3) epinephrine doses or IV epinephrine, and 13% experienced life-threatening reactions.
The findings highlight that although rare, iodinated contrast anaphylaxis can be persistent or recurrent, emphasizing the importance of rapid recognition and prompt treatment rather than relying mainly on premedication.
In the comprehensive 10-year review published in the Annals of Allergy, Asthma & Immunology, researchers from the Mayo Clinic, led by Hans Gao and colleagues, examined the true burden and severity patterns of anaphylactic reactions linked to iodinated contrast media (ICM) used during CT imaging. With global annual ICM use estimated at nearly 75 million doses, understanding the nature of these rare but potentially severe reactions remains a priority for clinicians across emergency, inpatient, and outpatient settings.
The team conducted a retrospective analysis of CT scans performed between January 2014 and November 2024, ultimately reviewing 702,917 scans that involved the administration of ICM. After a thorough manual chart assessment, 143 cases met the established criteria for anaphylaxis defined by the National Institute of Allergy and Infectious Diseases/Food Allergy and Anaphylaxis Network.
Key findings were as follows:
- The overall incidence of ICM-induced anaphylaxis was 20.3 cases per 100,000 scans, equivalent to 47.9 cases per 100,000 patients.
- Most reactions were monophasic, but the study also identified several complex and severe forms of anaphylaxis.
- Biphasic reactions, where symptoms reappear after initial improvement, occurred in 3% of cases.
- Refractory anaphylaxis was seen in 10% of patients and required three or more doses of epinephrine or an IV epinephrine infusion.
- Life-threatening reactions, classified as Dribin grade 5, were documented in 13% of cases, including one fatal event.
- This study is the first in the U.S. to specifically quantify biphasic, refractory, and life-threatening anaphylaxis linked to iodinated contrast media.
- Life-threatening reactions occurred at a rate of 2.7 per 100,000 scans, highlighting the need for rapid emergency response capabilities.
- Some patients developed anaphylaxis despite receiving premedication, indicating that preventive measures do not completely eliminate risk.
Another concerning observation was the underuse of epinephrine—despite being the first-line treatment for anaphylaxis—suggesting gaps in timely intervention. The study emphasizes that delays or hesitancy in administering epinephrine can contribute to prolonged or worsening reactions, particularly in refractory cases.
The authors concluded that although iodinated contrast anaphylaxis remains uncommon, a meaningful proportion of reactions escalate to severe or life-threatening levels. They advocate for heightened clinical vigilance during and immediately after contrast administration, along with better adherence to emergency treatment protocols. Improved awareness, rapid symptom recognition, and prompt epinephrine use, they stress, are key to preventing complications and reducing mortality associated with these unpredictable reactions.
Reference:
Gao, H., Lu, L., Neto, E. S., McDonald, J. S., McDonald, R. J., Mullan, A. F., Hagan, J. B., Li, J. T., & Campbell, R. L. (2025). Biphasic, Refractory, and Life-threatening Anaphylactic Reactions to Iodinated Contrast Media: A 10-Year Retrospective Analysis. Annals of Allergy, Asthma & Immunology. https://doi.org/10.1016/j.anai.2025.11.004
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