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MAG 3 (kidney) scan - in children

Patient information A-Z

This leaflet is to provide parents and carers information about MAG 3 scans including why this scan has been advised for your child, what the scan involves and advice for before and after the scan.

What is a MAG-3 scan?

A MAG 3 scan will identify the position and shape of your child’s kidneys location and will assess how well one kidney is functioning (working) compared to the other one. MAG 3 scans are also used to identify how well urine is leaving (draining) from the kidneys and so helps identify any blockage or obstruction that affects the flow of urine from the kidneys.

Diagram of the urinary system. Labelled: kidney, ureter, bladder, urethra
Most people have two kidneys which are located near the bottom edge of our ribs, one each side, at the back. Kidneys filter blood to remove wastes and excess water to make urine. Kidneys are also responsible for maintaining a vital balance of water, salts and minerals in our blood and they make hormones that help control blood pressure.

A chemical substance, called an isotope, is given by injection into one of your child’s veins. The scan is named after the chemical ‘mercaptoacetyltriglycine’ (MAG 3 for short), to which the isotope is attached. The isotope is absorbed by the kidneys where it then emits (gives out) a type of radiation called ‘gamma rays’. Your child will lay on a scanning bed and a camera will then be used to detect the gamma rays and turn them into pictures. It is important that your child lays still to achieve the clearest images.

Before the appointment

  • There is no need for your child to fast (‘starve’) for this test. To achieve the best images it is helpful that your child is well hydrated so, unless your child has an underlying problem which means they have to restrict their fluid intake, please encourage your child to have plenty of drink in the 30 minutes prior to the scan. If you have a baby, please bring a feed with you ore breast feed your baby when you arrive.
  • A tube of local anaesthetic cream (‘EMLA’ cream) may be sent to you in the post with your appointment letter. This cream needs to be applied one hour before the appointment onto four areas, each covering a vein. Apply onto the back of both of your child’s hands where you can see a vein and cover with the plasters included in the pack. Repeat on the inside of their arms over the bend of the elbow. Although you are asked to put the cream in four places, this does not mean your child will have four injections; it is to help the nurse choose which vein is the best.
  • There is a small risk that the isotope given to your child could harm an unborn baby. Therefore if you are pregnant or think you could be pregnant, please call us before the appointment is due for further advice as it may be necessary to reschedule the appointment.
  • If your daughter is 12 years or over we will ask her about her periods and any possibility that she could be pregnant.
  • If your child is apprehensive about needles or scans please inform us without delay before the day of the appointment so we can advise on how to prepare your child or amend arrangements for the appointment.

Preparing your child

  • Research has shown that children cope much better with hospital procedures if they are well prepared and informed of what is going to happen. It is therefore important for you to talk to your child and explain in a simple and positive manner about what will happen during their visit to the hospital.

Some terms that may help when preparing your child could be:

  • magic cream (EMLA). This cream stops the injection from stinging too much.
  • “while you are having your scan it is important to lie very still so that we do not get fuzzy pictures”
  • lying still for a story can be practiced at home; remember to bring your book in with you. Playing ‘sleeping lions’ can be a fun way to practice lying still.
  • it may be possible for your child to watch a DVD whilst lying still for imaging; you could bring one with you.

What to do if you cannot attend the appointment

Demand for appointments is high therefore, if the appointment is not convenient it is essential that you contact us without delay so we can both rearrange the appointment for your child and, offer the appointment you are unable to attend, to another patient on our waiting list.

If you do not contact us and then fail to attend the appointment a further appointment will not be offered. Your child’s Consultant or GP will be informed.

It is important that the adult accompanying your child for their MAG 3 scan has ‘parental responsibility’ that is, legal rights, responsibilities, duties, power and authority to make decisions for your child. If the person accompanying your child does not have parental responsibility the scan may need to be rearranged.

At the appointment

The MAG 3 scan takes place in the nuclear medicine department. Young children may be asked to attend one of our children’s wards before arriving at the nuclear medicine department so that one of our specialist children’s team can insert a temporary tube into the vein (called a ‘cannula’) which is then used to administer the isotope through. Please ensure that you arrive promptly at the appointment time; arriving late may result in the appointment needing to be re-scheduled.

On arrival your child will be weighed so the correct dose can be calculated.

You and your child will be shown to a room with a scanning bed which, can be moved so that the technician can get the scan in the right position. There is a camera under the scanning bed which takes a series of pictures of the kidneys and bladder. Above the scanning bed is a small screen on which it is possible to see a picture of the kidneys and bladder.

Your child will be asked to lie down whist they are given a small injection of the radioactive substance and then the needle is immediately removed. The scan starts as your child has the injection. It is necessary for your child to keep very still while the scans are taken and the technician can help with this. You will be able to stay with your child at all times and you may hold their hand. They may also bring a soft toy or a book can be read to them during the scanning process.

After a series of images have been taken, your child may be asked to empty their bladder into a container and then have another picture taken. This part of the test is called a ‘non direct micturating cystogram’. The technicians will leave the room and a screen provided to maintain your child’s privacy at this time. An indirect cystogram assesses whether there is reflux (back flow of urine) from the bladder back up to the kidneys.

Taking all the pictures usually takes approximately 20 to 30 minutes. Once all the pictures have been taken you and your child may go home. A consultant radiologist will send a report about the scan’s findings to your child’s care team.

For the 24 hours following the appointment

The radioactive substance lasts for only a short period of time and has usually disappeared from the body within 24 hours. During this time:

  • Encourage your child to take plenty of drink as this will help the isotope to pass out of their body quicker.
  • Toilet trained children should be encouraged to go to the toilet regularly. Hands must be washed thoroughly with soap and water.
  • If your child uses a potty, wash the potty and hands thoroughly with soapy water.
  • If your child wears nappies or pads, change them frequently and remember to wash hands thoroughly with soap and water.
  • If you are pregnant or think you may be pregnant, you should try to avoid contact with your child’s bodily fluids (urine, faeces and vomit) for 24 hours as much as possible and otherwise be thorough with hand washing.

Your child should continue to take any regular medications they receive as normal.

Risks and radiation

Gamma rays are one type of ionising radiation. We are all exposed to ionising radiation in our day to day lives; for example, it is in some construction materials and it seeps from the ground into buildings, when we eat certain foods and when we take a flight.

The isotope used in a MAG 3 scan contains a small amount of radioactivity, and the radiation from this will be similar to the amount your child normally experiences from a few months of natural background radiation.

The isotope becomes inactive in the hours after the scan and is passed out of your child’s body via their urine hence the precautions advised above in section ‘For the 24 hours following the appointment’.

There are no side effects from the scan itself and the isotope will not interfere with any medication that your child is taking.

Are there alternatives to a MAG 3 scan?

Although there are other tests (e.g. ultrasound and CT scans) which can assess the shape and size of your child’s kidneys, they are not able to assess kidney function or how well urine drains from the kidneys. Understanding kidney function and how well kidneys drain will be used to plan your child’s treatment.

For more information

The nuclear medicine department: 01223 217145

Paediatric urology nurse specialist: 01223 586973 (Monday to Friday, 08:00-18:00)

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

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Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151