Allergy to contrast dyes: symptoms, treatment, general information
An intravenous (IV) contrast dye allergy is a reaction to a substance, also called radiocontrast products (RCM), which is administered through a vein to get a better view of internal structures during medical imaging and scans.
Technically, contrast dye allergies are not allergies, but can produce serious allergy-like symptoms, such as skin reactions or difficulty breathing.
Most of these reactions occur within an hour of receiving contrast material and many occur within the first five minutes. However, sometimes there can be delayed reactions that occur up to a week later.
This article explores the types of contrast dyes used in imaging, risk factors for reactions, and how a contrast dye allergy is treated.
What is Contrast IV
IV contrast is a solution given through a vein that helps highlight structures, such as organs and blood vessels during imaging.
IV contrast is commonly used with:
Types of contrast dye
There are two main types, or classes, of IV contrast that are used. They are:
- Iodinated contrast dye contains iodine and is used in most CT scans and other types of imaging that use X-rays. Iodine helps get visuals inside hollow spaces, such as blood vessels and organs.
- Gadolinium-based contrast dye (GBCD) contains a rare earth metal called gadolinium which improves MRI scans.
The two types are quite different and not thought to be cross-reactive, which means that if you have a CT contrast dye reaction to iodinated contrast, that doesn’t necessarily mean you will have a contrast reaction. GBDC for an MRI.
However, always discuss any past reactions with your healthcare provider.
Within the iodinated contrast type, there are two main subtypes:
- Low osmolality non-ionic contrast agent (LOCM), meaning that iodine is bound to organic (nonionic) compounds and is more dilute
- High osmolality ionic contrast agent (HOCM), meaning that compounds can break into separate particles called ions and iodine is more concentrated
LOCM has become the preferred form of IV dye, given its better safety record. However, it is more expensive than HOCM.
to sum up
Iodine contrast dye which contains iodine is used for scans involving X-rays, such as CT scans. Gadolinium-based contrast is used for MRIs.
Types of reactions
Although severe reactions are often called contrast dye allergies, they are technically not allergic in nature. This is because there are usually no antibodies or specialized proteins designed to attack an allergen.
Rather, the contrast dye is thought to work to directly release chemicals, such as histamine, from immune cells that are part of the immune system, triggering allergy-like symptoms.
The severity of a contrast dye reaction can range from mild to severe and potentially life-threatening.
How common are reactions to contrast dye?
Mild reactions to contrast dye are fairly common, and serious reactions and side effects are rare.
The categories of reaction to the contrast dye are:
- Mild reactions are relatively common, occurring in 3 to 15% of people receiving contrast media. Most of these reactions include feeling hot, nausea, and vomiting. Typically, symptoms occur for a short time and do not require treatment.
- Moderate reactions may include severe vomiting, skin reactions and swelling, and occur in about 0.02% to 2% of people receiving contrast material. They require treatment.
- Severe reactions include anaphylaxis, a life-threatening emergency that can lead to difficulty breathing. Severe reactions occur in 0.04% to 0.02% of people receiving contrast material, with a fatality rate of 1 in 170,000 people.
Symptoms of a moderate or severe reaction requiring urgent medical attention include:
- Severe vomiting
- Difficulty breathing
- Swelling in the throat
- High-pitched sound when breathing
- rapid heartbeat
- Cardiac arrest, which is a sudden loss of consciousness, breathing, and pulse
The likelihood of a reaction to LOCM is much lower than with HOCM, and the likelihood of a reaction to gadolinium-based contrast (as used in MRIs) is even lower.
to sum up
Most contrast medium reactions are mild and do not require treatment. When moderate to severe reactions occur, symptoms may include severe vomiting, hives, or difficulty breathing, and require urgent medical attention.
These factors appear to put people at higher risk for adverse or allergic reactions to contrast media:
Older people also have an increased risk of severe reactions
The Seafood Myth
Despite popular myth, having a seafood and shellfish allergy does not put you at an increased risk of having a reaction to the contrast dye. Seafood allergy is due to the protein content of these foods, not the iodine content.
Also, if you are allergic to iodine-based topical cleansers or iodides, you are at no increased risk of reactions.
Unfortunately, there is no test available to diagnose a contrast dye allergy.
Skin tests and blood tests to check for allergies are often not helpful in diagnosis.
Reactions are unpredictable and small trial doses do not indicate whether or not a reaction will occur. There are reports of serious and life-threatening reactions to contrast dye occurring after a person has tolerated a small test dose of IV dye.
to sum up
An allergy to IV dyes can only be diagnosed after symptoms appear. Otherwise, it is only possible to determine that a person has an increased risk of a reaction.
The treatment of an allergic reaction is similar to that of an adverse reaction whatever the cause.
Treatment may include the following:
If you had a non-severe reaction to contrast dye and need to use a similar type for more imaging, your doctor will likely recommend premedication.
It is common to be treated with a premedicated combination of oral corticosteroids, such as prednisone, and antihistamines, such as Benadryl (diphenhydramine), before any imaging using a similar type of contrast.
Patients with a history of severe reactions should avoid the same class of contrast dye except in specific and serious circumstances under the direction of a healthcare professional.
IV contrast dye is a solution that is introduced into the bloodstream during medical imaging to highlight internal structures, such as organs and blood vessels.
The two main types of contrast are gadolinium-based contrast used for MRIs and iodinated contrast used for CT scans and other X-ray imaging.
Having a reaction to iodinated contrast does not mean that you will react to gadolinium-based contrast and vice versa.
Mild reactions to contrast dye are fairly common and do not require treatment. In rare cases, serious and life-threatening emergencies can occur.
A word from Verywell
If you are concerned about a potential reaction to contrast dye, talk to your healthcare professional about the risks and benefits of performing a contrast dye test and whether alternatives are available.
If you had a reaction to the contrast dye used during a CT scan and need imaging, your healthcare provider may be able to get similar information by doing an MRI, which uses a gadolinium-based contrast instead of iodinated contrast.
If a CT scan is needed, ask if LOCM rather than HOCM could be used.
If you have a history of serious reactions to contrast dye, this is usually avoided, so always tell your health care provider about any previous reactions.
Frequently Asked Questions
Are IV contrast dyes safe?
These are generally considered safe, but there is a risk of nephrogenic systemic fibrosis, a rare condition that primarily affects the skin, and contrast-induced nephropathy, which leads to loss of kidney function. These complications are more common in people with existing kidney disease. If you have a history of allergies, you may need to take medication before receiving the contrast medium to avoid a serious allergic reaction.
Is having a contrast product injected painful?
No. There may be some discomfort when inserting the IV line, but you shouldn’t feel any pain when the dye is injected. You may have some sensations, however:
- Feeling of warmth and redness through your body for a few seconds
- Metallic taste in the mouth
- You feel like you’re urinating, but you’re not
Can I have a contrast scan if I have food allergies?
Any history of allergy increases your risk of having a reaction to contrast agents. However, your healthcare provider may be able to provide you with medications you can take before an ultrasound to help prevent a reaction. While shellfish and seafood allergies are sometimes assumed to put you at particular risk of an iodine contrast reaction, there does not appear to be any evidence that this is true.