Iodine-based dye used to make X-ray and CT scans clearer
Iodinated contrast media
An iodine-based dye used to make X-ray, CT and angiography scans clearer; it is not a treatment.
What is Iodinated contrast media?
Iodinated contrast media are iodine-based dyes used during X-ray, CT and angiography scans to make blood vessels and organs show up more clearly, so doctors can see what is happening inside the body. They are usually injected into a vein, but can sometimes be swallowed. They are a diagnostic aid, not a treatment. The main safety concerns are allergic or allergic-type reactions, a risk of kidney injury (especially with poor kidney function or dehydration), the need to consider metformin around the scan, and possible effects on the thyroid.
Education and reference only. This is a plain-language guide to Iodinated contrast media — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Iodinated contrast media are special iodine-based dyes used during imaging tests such as X-rays, CT scans and angiography (pictures of blood vessels). They make blood vessels, organs and other structures stand out more clearly on the images, helping doctors find and assess problems. They are usually given as an injection into a vein during the scan, though sometimes they are swallowed to outline the gut. It is important to understand that contrast is a diagnostic tool to improve the pictures, not a medicine that treats any condition.
How it works
Iodine absorbs X-rays strongly, so wherever the contrast goes it shows up brighter on the scan. When injected into a vein, it travels through the bloodstream and highlights blood vessels and well-supplied organs, making it easier to see narrowings, blockages, swellings or other changes. When swallowed, it outlines the gut. The contrast does not change the body or treat anything; it simply makes the structures clearer for the few minutes the scan is being taken, after which the body gradually clears it, mostly through the kidneys.
Company & origin
Originated / developed by: Various manufacturers.
Iodine-based contrast agents used in hospitals and imaging centres across the UK to make X-ray, CT and angiography scans clearer.
Practical use
How to take Iodinated contrast media
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by trained staff during your scan, usually as an injection into a vein, sometimes as a drink.
- Tell the team about any previous reaction to contrast, allergies, asthma, or kidney or thyroid problems.
- Tell them if you take metformin for diabetes, as you may be advised to pause it around the scan.
- Drink fluids before and after as advised, to help your kidneys clear the contrast.
- Report any itching, rash, swelling, breathing difficulty or feeling unwell during or after the scan.
Weighing it up
Advantages & disadvantages of Iodinated contrast media
Advantages
- Makes blood vessels and organs show up clearly, helping doctors diagnose problems accurately.
- Quick to give during the scan and cleared by the body afterwards.
- Allows detailed pictures, such as of blood vessels, that would not be possible otherwise.
Disadvantages
- Can cause allergic or allergic-type reactions, occasionally severe.
- Can affect the kidneys, especially with poor kidney function or dehydration.
- Needs care around metformin and can affect the thyroid in some people.
Practical use
Good to know
The key point is that this is a dye to make scans clearer, not a treatment, and it is given by trained staff who watch closely for problems. The most important safety concern is reactions: most people have none, but allergic or allergic-type reactions can happen, ranging from mild flushing or itching to, rarely, severe reactions, so any previous reaction must be mentioned. The kidneys clear the contrast, so it can occasionally cause kidney injury, particularly in people whose kidneys already work poorly or who are dehydrated; staying well hydrated and checking kidney function beforehand help reduce this. People taking metformin for diabetes may be advised to pause it around the time of the scan, because of how the kidneys and metformin interact. Contrast can also affect the thyroid in some people. A warm flushing feeling as it is injected is common and harmless.
Who should not take it / use with caution
- People who have had a serious reaction to iodinated contrast before are given it only with great caution, if at all.
- It is used with care in people with poor kidney function, dehydration or certain thyroid problems.
- The team weighs the benefits and risks carefully in people with asthma or a strong history of allergies.
Monitoring
- Checking kidney function before the scan in those at risk.
- Watching closely during and after the scan for any allergic-type reaction.
- Reviewing thyroid function or metformin where appropriate after the scan.
Side effects
- A warm flushing feeling and a metallic taste as it is injected, which is common and harmless.
- Allergic or allergic-type reactions, from mild flushing or itching to, rarely, severe reactions.
- Kidney injury, especially with poor kidney function or dehydration, and occasionally thyroid effects.
Key interactions
- Metformin, taken for diabetes, may need to be paused around the scan because of kidney considerations.
- Some medicines and conditions that affect the kidneys can increase the risk of kidney injury.
- Tell the team about all your medicines and any thyroid treatment before the scan.
Available as: A solution injected into a vein, or sometimes a drink, given during imaging.
Answers
Iodinated contrast media: frequently asked questions
What is iodinated contrast for?
It is an iodine-based dye used during X-ray, CT and angiography scans to make blood vessels and organs show up clearly; it is not a treatment.
Is it dangerous?
Most people have no problems, but it can occasionally cause allergic-type reactions or affect the kidneys, so the team checks for risks and watches closely.
Why am I asked about metformin?
If you take metformin for diabetes you may be advised to pause it around the scan, because of how the kidneys and metformin interact.
Will I feel anything when it is injected?
A warm flushing feeling and sometimes a metallic taste are common and harmless as the contrast is injected.
Why do I need to drink fluids?
Staying well hydrated helps your kidneys clear the contrast and reduces the small risk of kidney injury.
Authoritative sources
- BNF
- NICE CKS
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