Published online: April 12, 2018
Injection of iodinated contrast media (ICM) allows high resolution imaging of blood vessels. Allergic reactions to ICM have been previously well described and may potentially entail severe or even fatal outcomes. The use of new generation ICM is thought to reduce allergic responses considerably, although their current prevalence is unclear. In patients already carrying a diagnosis of ICM allergy, anti-histamines and steroids are usually recommended prior to imaging. The capacity of this regimen to prevent adverse effects has often been questioned and calls for further evaluation.
In a recent article published in The Journal of Allergy and Clinical Immunology: In Practice, Topaz and colleagues retrospectively screened the medical records of 13,652 subjects admitted to the hospital for investigation of chest pain. They searched for patients who were referred to in-hospital percutaneous coronary intervention. This procedure involves the insertion of a catheter into the heart followed by injection of ICM to allow visualization of the arteries. Their aim was to identify allergic reactions during the procedure, to assess the significance of a prior diagnosis of allergy and to evaluate the benefit of pre-medication.
Nine hundred thirty-one individuals without prior ICM allergy were referred to coronary intervention, of whom two had minor allergic reactions. Previously diagnosed ICM allergy was recorded for 216 subjects, and 32 of them were referred to in-hospital coronary intervention. Pre-medication was administered in 10 cases only, with no documented rationale for not treating the other 22. Among these 32 individuals, only one allergic response was documented in a pre-treated patient. No mortality was observed in the 30 days following injection of ICM among the patients with known allergy.
This study shows that ICM allergy is rare, and that most patients with previously diagnosed allergy do not react to ICM. It is strongly recommended that these patients should undergo a formal allergic evaluation to rule out misdiagnosis. No advantage could be demonstrated for pre-medication and, therefore, it can probably be avoided in most patients. If administered, it should not cause considerable delays in imaging and medical procedures. Randomized controlled trials are warranted to determine whether the administration of pre-medication is justified, given its limited benefit and the multiple adverse effects of steroids. This work provides convincing evidence that such prospective trials are expected to be feasible and safe.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.