Allergies to IV Dye or Iodine Contrast

Doctor looking at image from coronary angiography

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In This Article

Intravenous (IV) dye (dye given through the vein)—also known as radiocontrast media (RCM)—is used widely in the United States for various radiological studies, such as angiograms, X-rays, magnetic resonance imaging (MRI), and computed tomography (CT) scans. Adverse reactions to RCM are fairly common, though allergies are rarer.

You may be surprised to learn that allergic 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.

Types of Radiocontrast Media

In general, there are two basic types of intravenous RCM used for most radiological studies. They include:

  • 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's more expensive than HOCM.

Types of Reactions

These are reactions that may occur when you've been administered RCM:

  • Mild reactions: These are relatively common, occurring in 3 to 15% of people receiving them. 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 don't require treatment.
  • Moderate reactions: These include severe vomiting, hives, and swelling, and occur in an estimated 0.02 to 2% of people receiving RCM. They frequently require treatment.
  • Severe, life-threatening reactions: This includes anaphylaxis, and these occur in 0.04 to .02% of people receiving RCM, with a death rate of one person in every 170,000.

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.

Risk Factors

These factors appear to put people at higher risk for reactions to RCM:

  • Past reactions to RCM
  • Asthma
  • History of allergies
  • History of heart disease
  • History of kidney disease
  • Taking beta-blockers
  • Females
  • Elderly (appear to be at higher risk for severe reactions)

The Seafood Myth

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


Unfortunately, there is no test available to diagnose an allergy to RCM. Skin testing and radioallergosorbent testing (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.

An IV-dye allergy can only be diagnosed after symptoms have occurred. Otherwise, it's only possible to determine that a person is at increased risk of a reaction.


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.


If you've had a reaction to RCM, preventing future RCM reactions should include the following steps.

Talk to your doctor about the risks and benefits of performing a test with RCM and whether alternatives are available. Use LOCM rather than HOCM. Take medicines prior to the administration of RCM to prevent or decrease the chance of reactions, including:

  • Prednisone, 50mg for an adult, orally taken at 13 hours, 7 hours, and 1 hour prior to receiving RCM
  • Diphenhydramine (Benadryl), 50mg for an adult, taken orally 1 hour prior to receiving RCM
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