Radiocontrast

Background

Modern radiocontrasts are non-ionic, iodinated and either iso-osmolal or low-osmolality. Older radiocontrasts were high-osmolality–which are no longer used intravenously.

The radiocontrast molecular structure is responsible for hypersensitivity reactions–not iodine or seafood allergy. Shellfish allergy is secondary to tropomyosin not iodine.

Infusion Reactions

These are also referred to as “toxic” or “chemotoxic” reactions. Characteristic symptoms include transient warmth/flushing, nausea/vomiting, chest pain, metallic taste, hypertension, and/or vasogal signs.

Immediate Hypersensitivity Reactions

The most common immediate hypersensitivity reaction to radiocontrast is mild urticaria and pruritus, occuring in ~0.9% - 3.1% of patients receiving radiocontrast. Anaphylaxis occurs in 0.02% - 0.04% of patients. Of immediate hypersensitivity reactions, 70% occur within 5 minutes of radiocontrast injection and 96% of severe reactions occur within 20 minutes.

Delayed Hypersensitivity Reactions

The most common delayed hypersensitivity reaction to radiocontrast is a maculopapular exanthem–occurring in 1 to 3% of patients.

Skin Testing

Skin prick testing to the culprit and other radiocontrasts followed by intradermal testing–if skin prick testing is negative–can be useful for identifying an alternative radiocontrast agent. A skin test negative radiocontrast alternative has a 95% NPV.

Intravenous Challenge

Intravenous challenge can be performed to radiocontrast with various protocols–such as 1 mL, 5 mL, 15, mL, and 50 mL (cumulative 71 mL) at 60 minute intervals.

Management

The culprit radiocontrast should be avoided, and an alternative radiocontrast should be used, guided by negative skin testing if available. Other measures to decrease risk of recurrent radiocontrast reaction include: lowering the radiocontrast dose, decreasing the injection speed, and pre-treatment with non-sedating, second generation antihistamines and/or corticosteroids.