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Iodine Contrast Allergy

Iodine Contrast Allergy


Updated May 23, 2014

Iodine Contrast Allergy

Intravenous contrast (IV) dye may be used to enhance the images of a ct, or "cat" scan, of various areas of the body. Reactions to IV dye are common, and can be life-threatening.

Updated May 23, 2014
Iodine Contrast Allergy

What is Radiocontrast Media?

Radiocontrast Media (RCM), or IV dye, is used more than 10 millions times each year in the United States for various radiological studies, such as angiograms, “cat” scans, and intravenous pyelograms (IVPs). In general, there are two basic types of RCM used for most radiological studies: Ionic high-osmolality contrast media (HOCM) and non-ionic low-osmolality contrast media (LOCM). LOCM has become the preferred form of IV dye in recent years, given its better safety record; however, it is far more expensive than HOCM.

Allergy to Radiocontrast Media

Reactions to RCM are relatively common, occurring in 5 to 8% of people receiving IV dye. Most of these reactions are mild, and include a feeling of warmth, nausea and vomiting. Generally, these symptoms occur only for a short period of time and do not require treatment. Moderate reactions, including severe vomiting, hives and swelling, occur in 1% of people receiving RCM, and frequently require treatment. Severe, life-threatening reactions, including anaphylaxis, occur in 0.1% of people receiving RCM, with an expected death rate of 1 person in every 75,000.

Reactions to LOCM are much lower than that of HOCM, although the most severe reactions, including death, have been reported to occur at similar rates with both types of contrast media.

Reactions to RCM are not truly allergic in nature, meaning that there is no allergic antibody present that causes the reaction. Rather, RCM acts to directly release histamine and other chemicals from mast cells.

Who Is At Risk for Allergy to Radiocontrast Media?

People who appear to be at higher risk for reactions to RCM include the following groups:
  • Those with past reactions to RCM (up to 44% chance of repeat reaction with future RCM administration)
  • People with asthma
  • History of allergies
  • History of heart disease
  • History of kidney disease
  • Those taking beta-blockers
  • Females
  • Elderly (appear to be at higher risk for severe reactions)

Despite the popular myth, having seafood and shellfish allergy does not place a person at increased risk of having a reaction to RCM. Shellfish allergy is due to the protein content of these foods, not the iodine content. In addition, those people with allergy to topical iodine cleaners or iodides are at no increased risk for reactions to RCM.

How Is Allergy to Radiocontrast Media Diagnosed?

Unfortunately, there is no test available to diagnose allergy to RCM. Skin testing and RAST have not been shown to be helpful in the diagnosis. Small, “test” doses are also not helpful, with reports of severe, life-threatening reactions occurring after small amounts of RCM given, as well as severe reactions with larger doses of RCM occurring after a person tolerates a small dose of IV dye.

Therefore, the diagnosis of RCM 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 RCM, based on the risk factors as outlined above.

How is Allergy to Radiocontrast Media Treated?

The treatment of an acute reaction to RCM is similar to that of anaphylaxis from any cause. Treatment may include injectable epinephrine and antihistamines, as well as the use of intravenous fluids for low blood pressure and shock.

The prevention of future RCM reactions should include the following:

  • Discuss with your doctor the risks and benefits of performing a test with RCM, and whether alternatives are available
  • The use of LOCM rather than HOCM
  • The use of medicines prior to the administration of RCM to prevent or decrease the chance of reactions, which may include:
    • Prednisone 50mg orally taken at 13, 7 and 1 hour prior to receiving RCM
    • Diphenhydramine (Benadryl) 50mg orally, intravenously or intramuscularly 1 hour prior to receiving RCM


Canter LM. Anaphylactoid Reactions to Radiocontrast Media. Allergy and Asthma Proc. 2005; 26:199-203.

Lieberman P, Kemp SF, Oppenheimer J, et al. The Diagnosis and Management of Anaphylaxis: An Updated Practice Parameter. J Allergy Clin Immunol. 2005; 115: S483-523.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

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