Contrast for CT and MRI: kidneys, allergy, breastfeeding

contrast dye · contrast agent · CT with contrast · MRI with contrast · contrast and kidneys

Contrast is a medicine given into a vein so the blood vessels and organs show up better on CT or MRI. For CT it is usually iodine-based, for MRI it is gadolinium-based.

When the doctor needs to see organs, tumors, inflammation, or blood vessels better.

⏱ Duration: the injection takes a minute, and the kidneys usually clear the contrast within a day

Be sure to tell your doctor

If you ever had a reaction to contrast
If you have asthma or a severe allergy
If you have kidney disease or are on dialysis
If you have diabetes and take sugar-lowering pills
If you might be pregnant or are breastfeeding
If you have thyroid disease, for CT

How to prepare

Test. A blood test for creatinine is often requested to check the kidneys.
Food. Sometimes you are asked not to eat for 2 to 4 hours. Check with the clinic.
Water. Unless your doctor limited it, drink plain water the day before and the day of the scan.
Medicines. Do not stop them on your own. If you take diabetes pills, your doctor will say what to do.

What to bring

The referral
Your creatinine test
Papers about a past reaction to contrast, if any
A list of your medicines

How it goes

Before the scan, you are asked about allergies and your kidneys
A thin line is placed in a vein in your arm
During the pictures, the contrast is given through the line
After the scan you are asked to sit for 15 to 30 minutes
The line is removed

What you'll feel

For CT: warmth through the body, a metallic taste, a feeling of needing the toilet
For MRI: usually nothing, or a cool feeling in the arm
These feelings pass within a minute

Afterwards

Drink more water that day, unless your doctor limited it
Breastfeeding after contrast is usually fine, but check with your doctor
With kidney disease, your doctor may order a test after the scan

Contact a doctor straight away if

A rash, itching, swelling of the face or lips, or trouble breathing: call emergency services
Severe pain, swelling, or redness at the injection site
Much less urine in the next days

Common questions

Can I breastfeed after contrast?

Usually yes, very little gets into the milk. If you are unsure, talk to your doctor.

What if I had an allergy to contrast?

Be sure to tell the staff beforehand. The doctor will decide whether to change the scan or give medicine first.

Is contrast harmful for the kidneys?

For healthy kidneys the risk is very small. With kidney disease, your doctor will weigh the benefit and risk beforehand.