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Ask The Expert

October 7, 2013

Skin Testing for Radio Contrast Allergens

Question

When would you recommend that the office-based practicing allergist should do skin testing for a patient requiring another study who had a moderately severe reaction?

Response

By Dr. Roland Solensky

Immediate-type reactions to RCM have traditionally been considered to be anaphylactoid, or non-IgE-mediated (also referred to as non-immunologic) mechanism. Pre-treatment regimens consisting of corticosteroids and antihistamines have been shown to be very effective in preventing the vast majority of reactions, and this is consistent with the reactions being non-IgE-mediated (such pretreatment should not prevent truly IgE-mediated reactions). Recent studies from Europe and Asia indicate that at least some immediate reactions to RCM may be IgE-mediated. This might be because nonionic media has replaced use of ionic media, and the former is less likely to result in direct non-IgE-mediated mast cell degranulation. I believe at this point, based on limited studies (some of which I summarize below), it is still unclear what proportion of reactions are IgE-mediated. Also, I am not aware of any studies in the US that have demonstrated positive skin tests with RCM.

Brockow et al (Brockow et al, Allergy 2009; 64:234-41) studied 122 patients with a history of immediate reactions to RCM. 32/126 (26%) were skin test-positive. Of those evaluated 2-6 months after the index reaction (which was felt to the ideal time to limit false negative tests performed too soon after reactions and not too late before IgE wanted), 14/28 (50%) were skin test-positive.

 Priesto-Garcia et al (Priesto-Garcia et al, J Investig Allergol Clin Immunol 2013; 23:183-9) is another large study of RCM from Europe. They studied 106 patients with immediate reactions to RCM and 11/106, or 10% were skin test-positive. Median time between reaction and skin testing was 4 months.

In Asia, Kim et al (Kim et al, Ann Allergy Asthma Immunol 2013; 110:258-62) evaluated skin testing prior to administration of RMC and found it had no clinical utility. Only one patient out of 1,048 had a positive immediate skin test, but there were 52 other skin test-negative patients who developed immediate reactions.

I believe available data indicate some reactions to RMC are IgE-mediated, but it is unclear what proportion of the total they comprise. We need more studies in which skin testing is utilized prior to administration of RCM, like the study by Kim et al, rather than just after a reaction has occurred. Also, importantly, we need studies on potential IgE-mediated reactions to RCM from the US.

I have not tried skin testing with RCM myself, and I'm not aware of anyone else in the United States who has tried. The unknown is whether someone who is skin test positive can be successfully pretreated to prevent reactions. If I encountered such a patient, I think an alternate agent shouldn't be difficult to find, so I would go with a different agent to which the patient is ST negative (so that would require skin testing with a 10-fold dilution of other agents. If a patient is ST negative, it is clear reactions still may occur based on those articles, so I would definitely still use pretreatment.

Roland Solensky, MD
Corvallis Clinic – Corvallis, Oregon, USA

 


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