Protocol eliminates or mitigates hypersensitivity reactions to iodinated contrast media
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Key takeaways:
- 84.8% of patients who followed the protocol completed CT scans without any adverse reaction.
- 53.3% of patients who did not follow the protocol experienced a recurrent reaction.
A two-track protocol helped physicians select safe iodinated contrast media for patients with immediate hypersensitivity reactions, according to a study published in The Journal of Allergy and Clinical Immunology: In Practice.
Patients who followed the protocol had lower rates of recurrence and reduced severity in recurrent cases, Ji-Hyang Lee, MD, PhD, of the department of allergy and clinical immunology at Asan Medical Center, University of Uslan College of Medicine, and colleagues wrote.
The study comprised 427 patients (mean age, 54.65 years; 61.6% women), including 349 (81.7%) who had been exposed to iodinated contrast media (ICM) a mean number of 5.45 times before experiencing an immediate hypersensitivity reaction (IHR). Causative agents included iohexol (Omnipaque, GE Healthcare; 23.4%), iopamidol (Pamiray, Dongkook Lifescience; 17.8%), iomeprol (Iomeron, Bracco; 17.8%), iobitridol (Xenetix, Guerbet; 13.6%), ioversol (Optiray, Guerbet; 12.6%), iopromide (Ultravist, Bayer Healthcare; 7.7%) and iodixanol (Visipaque, GE Healthcare; 7%).I
The protocol began with by taking each patient’s history of ICM hypersensitivity, followed by intradermal testing (IDT) with the causative ICM. Patients with negative skin tests then received premedication and a randomly changed ICM during their next CT examination.
Those with a positive IDT received additional skin tests with other available ICMs, and they underwent their next CT examination with premedication and an ICM that yielded a negative IDT. The protocol concluded with assessment of any IHR that may have followed.
With a mean time interval between the index event and skin test of 14.38 months, IDT using the causative agent yielded negative results for 283 patients (66.3%) and positive results for 144 patients (33.7%).
After undergoing the IDT, 86 patients with positive results and 213 with negative results were re-exposed to ICM. This group included 269 patients who followed the study protocol and 30 who did not.
The group that followed the protocol included 41 (15.2%) who experienced recurrent IHR and 228 (84.8%) who completed their CT scans without any adverse reactions.
Meanwhile, 16 patients (53.3%) who did not follow the protocol experienced an IHR. Thus, the protocol effectively prevented IHRs (P < .001), the researchers found.
Among the patients who did not follow the protocol, both patients who used an IDT-positive ICM experienced recurrence, as did 12 of the 16 patients (75%) who did not change the ICM and one of the 11 patients (9.1%) who did not receive premedication.
Among the 355 re-exposure cases, a greater proportion of patients who did vs. did not follow the protocol completed their re-exposure without an IHR (86.5% vs. 51.4%; P < .001).
Recurrence rates included 14.9% among patients whose previous reactions were mild, 13% among those whose previous reactions were moderate and 13.1% among those with severe previous reactions, with no statistical differences between these groups.
Breakthrough reaction rates in skin tests with culprit ICMs included 18.4% (14 of 76) in the IDT-positive group and 14% (27 of 193) in the IDT-negative group.
Also, iodixanol was prescribed in a greater proportion of cases that did vs. did not have repetitive IHR (34.2% vs. 15.8%; P = .005).
Among those who followed the protocol, percentages of moderate and severe cases decreased significantly from the index to recurrent reactions, while the percentage of mild cases increased (P = .003 with American College of Radiology criteria and P = .013 with Brown’s criteria). Conversely, IHR severity did not change significantly among the patients who did not follow the protocol.
Finally, with 237 patients getting skin tests with at least two different ICMs, cross-reactivity included iohexol and ioversol (21.9%), ioversol and iomeprol (19%) and ioemprol and iohexol (18.1%), with greater than 10% cross-reactivity between iohexol and the other six ICMs that were tested.
Based on these findings, the researchers concluded that their protocol reduced the recurrence of IHRs by 85.8% among patients with previous reactions and mitigated the severity of hypersensitivity reactions when recurrent cases did happen.
Perspective
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This study is interesting because it is prospective, whereas most contrast studies are retrospective. The big issue with these studies is that it is difficult to obtain materials for skin testing, and most places have one or two contrasts available. So, carrying out this protocol would be practically difficult.
The data on switching contrast prior to skin testing are decent, so I am not sure adding a skin test step is helpful compared with just switching contrast agents. The reaction reduction may be just as good with switching contrast. The other issue is that there are not enough allergists who would do this for timely information, so switching contrast is pragmatically easier.
Before incorporating this or similar protocols for testing patients with previous reactions, other practices would have to have an easier way to obtain materials for skin testing. There also would need to be “cross talk” between allergy and immunology specialists and radiologists.
As for the next step be in this research, a prospective article comparing this skin testing with contrast switching without skin testing would be optimal.
Perspective
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Allergic reactions to ICMs are uncommon (0.6% aggregate, 0.04% severe), although they represent a substantial risk to a subset of the population displaying previous allergic-like reactions including IgE-mediated hypersensitivities who have an approximately fivefold increased risk for developing a future reaction if exposed to the same ICM.
These patients are routinely premedicated or undergo alternative imaging when another ICM exposure is required.
The authors propose a new IDT management protocol for patients with prior IHR requiring re-exposure to IV iodinated contrast. The study design and statistical methods are valid, well executed and thorough, and the work represents a significant contribution to the literature on this topic.
However, practical, widespread implementation of the protocol in general radiology and medical practices is a significant concern. Iomeprol is available on a limited temporary basis in the U.S. (approved in 2022 during ICM shortages), and iobitridol is currently unavailable in the U.S., although the protocol can be modified excluding these agents.
Larger issues are the monetary and time costs for allergist referrals, multiple additional skin tests and likely increasing number of patients with contrast reactions based on an aging population and imaging utilization.
Medical and imaging practices must now operate at optimum efficiency and most choose one or sometimes two different ICMs for all procedures. In order to accurately assess the widespread applicability of this approach, a cost analysis examining patient and health care costs compared with potential patient significant adverse event reductions is needed.
Although the study is interesting and well designed, prospective comparison of the proposed protocol with the current premedication-only standard and premedication plus ICM change in prior moderate and severe allergic-like reactions aimed at achieving a more specific patient selection is necessary before adopting significant changes to existing recommendations addressing this impactful health care issue.
References:
ACR Manual on Contrast Media. https://www.acr.org/-/media/ACR/Files/Clinical-Resources/Contrast_Media.pdf. Published 2023. Accessed Oct. 26, 2023.
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