Skin Testing Helpful in Patients With Radiocontrast-Media Hypersensitivity

NEW YORK (Reuters Health) - Skin testing can be used to differentiate allergy from non-allergic reactions in patients with hypersensitivity to radiocontrast media (RCM) and to identify an alternative, safe RCM, researchers from Germany report.

Hypersensitivity reactions following intravascular injection of RCM are common, but genuine IgE-mediated RCM allergy is rare.

Dr. Axel Trautmann of the University Hospital Wurzburg and colleagues used data from 45 consecutive patients with a history of RCM hypersensitivity reactions to assess whether skin and provocation testing can differentiate between nonallergic and allergic hypersensitivity by identifying the causative contrast agent as well as a tolerated alternative agent.

Intradermal testing of 1:10 dilutions of the original contrast solution identified 21 patients as having nonallergic hypersensitivity (i.e., common skin test-negative); 11 patients had immediate-type allergy; and 13 patients had delayed-type allergy.

Two patients had borderline test reactions using standard 1:10 dilutions of iopromide and iopamidol, but subsequent testing of a 1:100 dilution was clearly negative, the researchers report in The Journal of Allergy and Clinical Immunology: In Practice, online April 10.

Two patients with clear-cut histories of maculopapular eruptions (MPE) tested negative for the culprit RCM but were unequivocally positive when tested with iodine tincture. The other 11 patients with a history of RCM-induced MPE tested negative with iodine solutions.

Of the 22 patients with true RCM allergy, all 18 tested patients tolerated intravenous provocation with a skin test-negative alternative contrast agent.

"The diagnostic sensitivity of intradermal RCM testing to identify allergic patients is high in both immediate-type and delayed-type RCM allergy," the researchers conclude. "Intravenous provocation with a skin test-negative RCM is safe and enables identification of a tolerated alternative RCM."

Dr. Eric M. Macy of the University of California, San Diego, who recently reviewed the epidemiology and management of RCM-associated hypersensitivity, told Reuters Health by email, "It is not possible to have an IgE-mediated allergy to the ion, iodine. Iodine is an essential element for all humans to ingest to enable proper thyroid function. Delayed-onset dose-dependent skin eruptions may occur with high-dose iodine ingestion or infusion, but this should not be called allergy."

"Iohexol and iodixanol are the two non-ionic radiocontrast materials most widely used in the United States," he said. "A much more practical approach in the United States is to just give an alternative non-ionic contrast to a patient with a reaction to a non-ionic contrast and skip any testing or premedication. Cross-reactivity is not that common between iohexol and iodixanol."

Dr. Karen S. Hsu Blatman from Brigham and Women's Hospital and Harvard Medical School, in Chestnut Hill, Massachusetts, has studied the management of hypersensitivity to RCM.

"If a patient developed a severe reaction to radiocontrast, beyond hives and swelling, skin testing to the RCM used and an alternative agent may be helpful," she told Reuters Health by email. "We would still default to a combination of systemic steroids and antihistamine for an urgent/emergency setting."

Dr. Ana Rosado Ingelmo from Hospital Universitario Fundacion Alcorcon, in Madrid, who participated in the development of Spanish clinical practice guidelines for diagnosis and management of hypersensitivity reactions to contrast media, told Reuters Health by email, "An important message for physicians is that all the patients who suffer an adverse reaction have to be studied, because in the future they can need those RCM again."

Dr. Trautmann did not respond to a request for comments.

SOURCE: https://bit.ly/2V8OPJX

J Allergy Clin Immunol Pract 2019.

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Benjamin Hidalgo-Matlock
Skin Care Physicians of Costa Rica

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