Hypersensitivity to IV contrast dyes

Intravenous (IV) contrast dye allergy is a reaction to a substance given through a vein to better visualize internal structures during medical imaging and scans.

Technically, a contrast dye allergy is not a true allergy. However, they can produce severe allergy-like symptoms, such as skin reactions or difficulty breathing.

Most of these reactions occurred within an hour of receiving the contrast dye, with many within the first five minutes. However, sometimes a delayed reaction may occur after a week.

This article will explore the types of contrast dyes (also known as radiocontrastor RCM), risk factors for reaction, and how to treat contrast dye allergy.

What is IV contrast?

IV contrast is a solution given through a vein to help highlight structures such as organs and blood vessels and distinguish them from other tissues during imaging. This enables the radiologist (the professional who reads the scan) to view the area of ​​interest in more detail.

IV contrast agents are often used to:

  • A computed tomography (CT) scan, which uses a series of X-rays and a computer to look at structures in the body.
  • Magnetic Resonance Imaging (MRI), which uses a magnetic field and a computer to create images
  • Angiography, where X-rays examine the path of contrast agents through blood vessels

Types of contrast dyes

There are two main types or classes of IV contrast media used – iodinated contrast media and gadolinium-based contrast media.

Iodinated Contrast Dyes Contains iodine, used in most CT scans and other types of imaging involving X-rays. Iodine helps achieve visual effects in hollow spaces such as blood vessels and organs.

This class has two main subtypes:

  • Nonionic low osmolarity contrast media (LOCM): Iodine is combined with organic (non-ionic) compounds at higher dilution.
  • ionic hyperosmolar contrast media (HOCM): These compounds can be broken down into individual particles, called ions, with higher concentrations of iodine.

Given its better safety record, LOCM has become the preferred form of IV dye. However, it is more expensive than HOCM.

Gadolinium based contrast dyes (GBCD) contains rare earth metals for enhanced MRI scans.

The two main types are completely different. Responding to one does not necessarily mean that you will react to the other.

However, you should always discuss all previous reactions with your healthcare provider.


Iodine-containing iodinated contrast dyes are used in scans involving X-rays, such as CT scans. Gadolinium-based contrast is used in MRI. Responding to one type does not necessarily mean that you will react to the other.

Types of contrast dye reactions

Medically speaking, not everything that looks like an allergic reaction is a real allergic reaction. This is the case with a reaction known as a contrast dye allergy.

Allergic reactions are accompanied by the production of antibodies or immune proteins designed to attack allergens. This does not happen with contrast dye reactions.

Instead, it is thought that contrast dyes work by releasing chemicals, such as histamine, directly from immune cells. This can trigger allergy-like symptoms.

Contrast dye reactions can range in severity from mild to severe and even life-threatening.

The likelihood of a response to LOCM is much lower than that of HOCM, and even lower to gadolinium-based contrast agents such as those used in MRI.

mild reaction

Mild reactions are relatively common, occurring in 3% to 15% of people receiving contrast.

Most of these reactions include:

  • a warm feeling
  • nausea
  • Vomit

Generally, symptoms appear within a short period of time and do not require treatment.

moderate to severe reaction

Moderate reactions include severe vomiting, skin reactions, and swelling, and about 0.02% to 2% of people receive contrast. They need treatment.

Severe reactions include anaphylaxis, a life-threatening emergency that can cause difficulty breathing. Serious reactions occurred in 0.04% to 0.02% of those who received contrast, and 1 in 170,000 people died.

Symptoms of a moderate or severe reaction requiring urgent medical attention include:

  • severe vomiting
  • measles
  • Difficulty breathing
  • swollen throat
  • high-pitched sound when breathing
  • twitch
  • fast heart rate
  • Cardiac arrest, which is a sudden loss of consciousness, breathing, and pulse


Most reactions to contrast dyes are mild and do not require treatment. When a moderate to severe reaction occurs, symptoms may include severe vomiting, hives, or difficulty breathing. Urgent medical care is required.

Symptoms of Anaphylactic Shock

risk factor

These factors appear to put people at a higher risk for adverse or allergic reactions to contrast dyes:

  • past responses to similar contrasts
  • asthma
  • allergy
  • heart disease
  • kidney disease
  • taking beta-blockers, which are commonly used to treat a variety of conditions, including heart disease

Older adults are also at increased risk for severe reactions.

seafood myth

Despite popular myths, being allergic to seafood does not put you at increased risk for a reaction to contrast dyes. Shellfish allergies are due to the protein content of these foods, not the iodine content.

Also, your risk of these reactions is not increased if you are allergic to topical iodine cleansers or iodide.


Unfortunately, there are no tests available to diagnose contrast dye allergy.

Skin tests and blood tests to look for allergies are often not helpful in diagnosis.

Responses are unpredictable, and trials with small doses do not indicate whether a response will occur when given in conventional doses. There have been reports of severe, life-threatening contrast dye reactions after a person has tolerated small doses of intravenous dye.


IV dye allergy can only be diagnosed after symptoms appear. Otherwise, only a person can be identified as having an increased risk of the reaction.


Treatment of allergic reactions is similar to adverse reactions from any cause.

Treatment may include the following:

  • Injectable epinephrine, which relaxes the tubes in the lungs called bronchi, making breathing easier
  • Antihistamines, drugs that block the effects of histamine
  • Intravenous fluids for hypotension and shock

Premedication for Contrast Allergy

If you have a non-serious reaction to the contrast medium and need more imaging with a similar type of contrast medium, your healthcare provider may recommend premedication. This involves taking medication before receiving a contrast dye to reduce the risk of a reaction.

Treatment is usually with a pre-drug combination of oral corticosteroids, such as prednisoneand antihistamines such as Benadryl (Diphenhydramine).

The same class of contrast dye should be avoided in patients with a history of severe reactions unless specific, serious conditions arise as directed by a healthcare provider.


IV contrast dye is a solution added to blood during medical imaging to make internal structures like organs and blood vessels easier to see.

The two main types of contrast agents are gadolinium, which is used in MRI, and iodine, which is used in CT scans and other X-ray imaging.

Responding to iodinated contrast does not mean you will respond to gadolinium-based contrast, and vice versa.

Mild reactions to contrast dyes are fairly common and do not require treatment. In rare cases, a serious and life-threatening emergency can occur.

VigorTip words

If you are concerned about a potential reaction to a contrast dye, talk with your healthcare provider about the risks and benefits of having a contrast test and whether there are alternatives.

If you have a reaction to the contrast agent used during a CT scan and need imaging, your healthcare provider may be able to obtain similar information by performing an MRI scan that uses a gadolinium-based contrast agent instead of an iodine-based contrast agent.

If a CT scan is required, ask if LOCM can be used instead of HOCM.

This is usually avoided if you have a history of severe reactions to contrast dyes, so be sure to let your healthcare provider know about any previous reactions.

Frequently Asked Questions

  • Are IV contrast dyes safe?

    These are generally considered safe, but carry a risk of nephrogenic systemic fibrosis (a rare disease that primarily affects the skin) and contrast-induced kidney disease (leading to loss of kidney function). These complications are most common in people with kidney disease. If you have a history of allergies, you may need to take medication before receiving the contrast dye to prevent a serious allergic reaction.

    understand more:

    Symptoms of kidney disease

  • How common are contrast dye reactions?

    Mild reactions to contrast dyes are somewhat common, serious reactions and side effects are rare.

  • Is it painful to inject contrast dye?

    Will not. There may be some discomfort when the IV tube is inserted, but you will not feel pain when the dye is injected. However, you may have some feelings. These include:

    • After a few seconds, your body feels warm and flushed
    • metallic taste in the mouth
    • itching
    • Feels like you’re urinating but you’re not

    understand more:

    Risks and Benefits of Different Types of Scans

  • Can I have a contrast dye scan if I have a food allergy?

    Any history of allergies increases your risk of having a reaction to contrast media. However, your healthcare provider may offer medications you can take before the scan to help prevent a reaction. While shellfish and seafood allergies are sometimes thought to put you at particular risk for a reaction to iodinated contrast, there seems to be no evidence that this is true.

    understand more:

    What you need to know about the most common allergies