Radiocontrast Media Allergy Diagnosis

Skin testing and RAST (radioallergosorbent test) have not been helpful in the diagnosis of contrast media allergy. Small “test” doses are also not helpful, with reports of severe, life-threatening reactions occurring even at such amounts. Severe reactions to larger doses of contrast media have been observed after a person tolerated a small dose of IV dye. Therefore, the diagnosis of contrast media allergy is made only after symptoms have occurred. Otherwise, it is only possible to determine that a person is at increased risk of a reaction to contrast media based on the risk factors outlined below.6


Allergy Prevention and Treatment

As mentioned above, the purpose of using these contrast agents is for diagnosis, but like any medical procedure in any radiological study, the right dose or volume of contrast media needs to be determined prior to a procedure. The total volume or dose is dependent upon several factors: iodine concentration of the contrast media; type of injectable contrast media (ionic or nonionic); patient’s body weight, anatomical structures or regions; speed of the injection; and age or disease process that could increase the risk of an adverse reaction. The treatment of an acute reaction to contrast media is no different from any other anaphylactic reaction. Treatment may include injectable epinephrine and antihistamines, as well as the use of IV fluids for low blood pressure and shock.7

Contrast media reactions can be prevented by a test dose for the intended contrast or the use of an alternative; the use of nonionic versus ionic media if applicable; and the use of certain medicines prior to the administration of contrast media such as prednisone 50 mg orally taken at 13, 7, and 1 hour prior to procedure, or diphenhydramine (Benadryl) 50 mg orally, IV or intramuscularly, 1 hour prior to receiving radiocontrast media.7


Risk Factors

As mentioned above, people who have seafood allergy are not at risk if they need to use contrast media. In addition, people with an allergy to topical iodine cleaners or iodides are also not at increased risk for reactions to contrast media. Patients who are at higher risk include those with past reactions to contrast media (up to 44%); those with asthma; those who have a history of heart and kidney and thyroid (both hypo- and hyperthyroidism) diseases; those taking beta-blockers or metformin; and females and the elderly (appear to be at higher risk for severe reactions).8,11