'Iodine allergy' label is misleading - Australian Prescriber

Constance H Katelaris, Professor, Clinical Immunology and Allergy, University of Western Sydney, and Campbelltown Hospital, Sydney; and William B Smith, Specialist, Clinical Immunology and Allergy, Royal Adelaide Hospital

Summary
'Iodine allergy' is not an accurate label for patients who have had allergic reactions to iodinated radiological contrast media or iodinated antiseptics. Allergy to seafood has nothing to do with iodine content as it is caused by specific immunoglobulin E to proteins. Seafood allergy is not a specific risk factor for reactivity to iodinated radiological contrast media, but a history of any moderate or severe allergic disorder confers a slight increase in risk. Patients with a previous history of allergy to radiological contrast media are at highest risk of a reaction. In some cases the risk of an allergic reaction to contrast media can be reduced by premedication, but, if previous reactions were severe, contrast media will usually remain contraindicated.

Key words: anaphylaxis, contrast media, seafood allergy.

(Aust Prescr 2009;32:125-8)

Introduction

The term 'iodine allergy' is used frequently and usually refers to a history of an allergic reaction to iodinated radiological contrast media or possibly a contact allergy to povidone-iodine. A misconception has arisen that allergy to seafood is caused by the iodine content of fish and shellfish. In a survey of patients presenting to a paediatric clinic because of suspected seafood allergy, 92% of the parents or patients believed that it was iodine in seafood that was the cause of the allergy.1

As a result, a history of seafood allergy is frequently considered to be a contraindication to the use of iodinated radiological contrast media. In a recent survey of radiologists and cardiologists in the USA, over 50% said that a history of seafood or shellfish allergy was sought before the administration of contrast media. One-third of the radiologists and 50% of cardiologists stated that they would withhold contrast media or recommend premedication if there was a history of sensitivity to seafood.2 Anecdotally, this is also often the case in Australia.

There is significant misunderstanding and confusion regarding seafood allergy, contrast media sensitivity and the role of iodine.

This is clinically important because patients may be denied useful procedures unnecessarily, while true risk factors may not be given due consideration resulting in the correct risk management procedures not being undertaken.

This article can be viewed in full at http://www.australianprescriber.com/magazine/32/5/125/8/