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.
Dr. Kenneth Backman of Allergy & Asthma Care comments: "This study demonstrates the effectiveness of a testing protocol in dramatically reducing the risk of recurrent reactions to iodinated contrast media (CT scan dye. While most allergy practices do not have access to these contrast media to perform these tests, academic centers should be able to implement this protocol to protect patients with a history of iodinated contrast media reactions."
