A MAG3 scan is a type of imaging test that uses special equipment to look at the structure and function of the urinary system.
This topic gives general information. The way these tests are performed will vary between different hospitals.
What is a MAG3 scan?
A chemical called mercaptoacetyltriglycine (MAG3 or MAG III) is injected into your child’s body. MAG3 is linked to a radioisotope. It emits (gives out) a type of radiation (source of energy) called gamma rays.
MAG3 is taken up in the kidneys and passed out into the urine. The camera detects gamma rays emitted from the MAG3 as it is taken up in the kidneys and flows out of the kidneys in the urine to the bladder.
Why does my child need this test?
The MAG3 scan is used to find out how well each kidney is working (the kidney function). It also shows how well urine is leaving, or draining from, your child’s kidneys. This may help to find out whether there is a blockage that affects the flow of urine from their kidneys, such as pelvic-ureteric junction (PUJ) dysfunction and obstruction.
The scan can also be used to check whether the flow of urine from the bladder goes up the wrong way in vesicoureteral reflux (VUR).
It can be used as an alternative to a micturating cystourethrogram (MCUG) if your child is old enough to empty their bladder when asked to.
Are MAG3 scans safe?
MAG3 scans use gamma rays which are a type of ionising radiation, a form of energy. We are all exposed to ionising radiation – in our homes and workplaces (it is in some construction materials and it seeps from the ground into buildings), when we eat certain foods and when go on an aeroplane.
At high levels, ionising radiation can be dangerous because it can damage cells, the living parts of the body.
A MAG3 scan uses a small amount of radiation so is considered safe. The chemical that is injected into your child’s body becomes inactive after a few hours and is passed out of their body in urine or faeces (poo).
Your doctor will carefully consider the risks and benefits of doing this test in your child.
How to prepare your child for a MAG3 scan
Your child does not usually need to do anything to prepare for this test, but your doctor will let you know if anything is needed.
Your doctor may ask whether your child has allergies to any medicines or contrast dye that may be used during the test.
Older girls may be asked if they are having their period, and about the dates of their last period. They may also be asked if they are pregnant or if they could be pregnant. This is because ionising radiation from X-rays may harm an unborn baby.
Tell your child’s doctor if you are pregnant as you may need to ask someone else to bring your child in for the scan.
Your child may be able to meet with a play specialist, who can use toys to help them prepare for the test.
What happens during the scan?
The MAG3 scan takes place in the nuclear medicine department of your hospital. It is performed by a radiographer (a specialist trained in imaging tests) or a technician.
This test usually takes about half an hour, though it may be longer.
The radioisotope is injected into a blood vessel, using a needle or a small plastic tube called a cannula. This is usually in the hand, arm or foot. Your child may feel a sharp scratch from the needle. A local anaesthetic, a spray or cream, can be put on your child’s skin before inserting the needle or cannula, to stop your child feeling any pain.
During the scan, your child lies on a scanning bed. They need to lie very still while a large camera above them takes pictures. These show the radioisotope moving through their kidneys.
Indirect cystogram
Occasionally the MAG3 test is extended to include an indirect cystogram. This involves taking images of your child’s bladder as it empties, to see whether there is reflux (backward flow) of urine back up to their kidneys. An indirect cystogram can be done in children who can control their bladder.
Direct cystogram
A direct cystogram also uses the MAG3 radioisotope to look directly for urine reflux. In the UK this is only very rarely used. The MAG3 isotope is injected into the bladder, either directly or through a catheter into the bladder, and images are taken as the child passes urine.
What to expect afterwards
Your child can usually go home straight away.
They may be asked to drink lots of water after the test. This will help ‘flush out’ the MAG3 from their body more quickly.
There may be a small amount of MAG3 in your child’s urine for 24 hours after the test.
Your child should sit on the toilet to urinate (wee) for the day after the test. Make sure they wash their hands with water and soap.
If your child uses nappies, put used nappies in a separate bag for 24 hours, then throw them away in your normal rubbish. Remember to wash your hands with water and soap.
If your child accidentally wets their clothes or bedding, put these in a separate bag for 24 hours and then wash them as normal.
Pregnant women should avoid direct contact with the child’s urine or poo for 24 hours.
Getting the results
A report will be sent to your doctor, who will discuss the results with you.