Overview of Allergies to IV Dye

How can reactions to iodine contrast be prevented?

Two Doctors with Patient at CAT Scan

IV dye (dye given through the vein)—also known as Radiocontrast Media (RCM)—is used more than 10 million 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)
  • 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.

    What Allergic Reactions May Occur with IV Dye?

    Reactions to RCM are relatively common, occurring in 5 to 8 percent of people receiving it. 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 percent of people receiving RCM and frequently require treatment.

    Severe, life-threatening reactions, including anaphylaxis, occur in 0.1 percent of people receiving RCM, with an expected death rate of 1 person in every 75,000.

    The likelihood of a reaction to LOCM is much lower than that with HOCM. Although the most severe reactions, including death, have been reported to occur at similar rates with both types of contrast media.

    You may be surprised to learn that 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 IV Dye?

    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 percent chance of repeat reaction with future RCM administration)
    • People with asthma
    • History of allergies
    • History of heart disease
    • History of kidney disease
    • People taking beta-blockers
    • Females
    • Elderly (appear to be at higher risk for severe reactions)

    Despite the popular myth, having a seafood and shellfish allergy does not place a person at an 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 an allergy to topical iodine cleaners or iodides are at no increased risk for reactions to RCM.

    How Is Allergy to IV Dye Diagnosed?

    Unfortunately, there is no test available to diagnose an 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 IV Dye 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.

    Preventing a Reaction to IV Dye

    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. These medications 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 et al. Anaphylaxis--a practice parameter update 2015. Ann Allergy Asthma Immunol. 2015 Nov;115(5):341-84.

      Schabelman E, Witting M. The relationship of radiocontrast, iodine, and seafood allergies: a medical myth exposed. ​​J Emerg Med. 2010 Nov;39(5):701-7.

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