This page is about your MAG3 renogram at Royal Brompton Hospital. It tells you about the scan, what will happen at your appointment and what to expect on the day. 

A MAG3 renogram shows how well your kidneys are working and how urine flows from the kidneys into the bladder. It helps your specialist understand whether there are any blockages, delays or changes in kidney function.

We know that having a scan can feel worrying. This page explains what will happen, how to prepare, and what to expect on the day. Our team will support you throughout your visit.

What the scan involves

We use a small amount of radioactivity, called a ‘tracer’, which is attached to a substance called MAG3. Your kidneys absorb this, allowing us to see how urine flows from the kidneys into the bladder.

The tracer is injected while you are lying on a couch. This tracer is taken up by the kidneys and shows how urine flows from the kidneys into the bladder. Images are taken straight away using a gamma camera positioned underneath the couch. The camera then takes continuous images for about 20 minutes.

The tracer does not cause any side effects.

What will happen on the day

When you arrive

• A technologist will explain the procedure and answer any questions. 
• A small needle (cannula) will be placed into a vein in your arm or hand.
• You will be helped into a comfortable position on the scanning couch.
• Some patients may be given a diuretic (a medicine that helps the kidneys work harder) about 15 minutes before the scan.
• If your clothing has metal fastenings that cannot be removed, we may ask you to change into a gown.

During the scan

• The tracer will be injected whilst you are lying down.
• The gamma camera will take images for about 20 minutes.
• You will need to lie still, but you can breathe normally.
• The scanner is similar in size to a CT scanner and quieter than an MRI scanner.

After the main scan

• You will be asked to empty your bladder.
• A final image will be taken. This takes about 1 minute.
• In some cases, an extra image may be taken after one hour.

How to prepare

• You can eat normally before the scan.
• You can continue taking your usual medicines unless your doctor has advised otherwise.
• Please drink plenty of fluids before you come for the scan.
• Drinking fluids and emptying your bladder regularly helps your body clear any excess tracer.

Risks of radiation during a MAG3 renogram

The amount of radiation used during a MAG3 renogram scan is small and kept to a minimum. We believe that the benefits of having the scan far outweigh any risks.

The risk of a person getting cancer because of this radiation is very low, 1 in 100,000 to 1 in 10,000 people. This level of risk is very small compared with the overall lifetime chance of getting cancer. The overall lifetime chance of getting cancer is around 1 in 2 people. 

After the scan

• A doctor will check the images while you wait.
• Once the images are confirmed, you can go home.
• The radiation dose from this scan is very small.
• You do not need to change your routine. There are no contact restrictions after this scan. 
• The tracer will not make you sleepy.
• You can drive and return to normal activities.

Your results

A nuclear medicine consultant will review your scan and send the report to your referring specialist. The results will also be available on the hospital’s electronic system.

Your specialist doctor will discuss the results with you and explain any next steps.