Glomerular filtration rate (GFR) scan

What is a renal scan and GFR?

A renal scan and GFR (glomerular filtration rate) is a test to look at how well the kidneys filter blood.

How long does the test take?

The test can take about three hours in total. This includes the time to inject your child, do the scan of their kidneys and wait for the blood samples to be taken. Please add half an hour to the total time if your child has a topical anaesthetic before the injection.

Does the test carry any risks?

A renal scan involves giving a very small amount of radiation to your child. The nuclear medicine team will discuss this with you when you and your child arrive for the X-ray. You might also find it helpful to read this information about nuclear medicine from the Alliance for Radiation Safety in Pediatric Imaging.

Does my child need to do anything special to prepare for the test?

Your child can eat and drink as usual, but they may be asked to drink one or two extra glasses of water or juice before the scan so they are well hydrated.

Some children need a blood or urine test before the test. Your doctor's office will tell you if your child needs one.

Will I be able to stay with my child during the test?

One parent or guardian may stay in the room with the child, but no other children are allowed.

How is the test done?

The test is done by a nuclear medicine technologist. It has four parts.

1. Your child will be given a small injection (needle) into a vein in the arm or back of hand.
2. The technologist will do a scan to take pictures of your child's kidneys.
3. The technologist will take a blood sample 1.5 hours after the injection.
4. The technologist will take a second blood sample 2.5 hours after the injection.

Injection

The injection contains a very small amount of radioactive medicine that mixes with the blood.

Note: The injection before the scan is not painful, but your child's hand or arm can still be numbed first with a topical anaesthetic (a special cream or cooling spray). If you would like this option, it is best to arrive at least 30 minutes before your appointment time to allow the anaesthetic to take effect.

Scan

Your child will then lie down on a narrow bed and a special camera will take pictures for 30 minutes right after the injection. This is to see how your child's kidneys filter the medicine. In most cases your child can watch a movie as the scan is being done.

Blood samples

The blood samples are taken to check how well the kidneys can remove waste products at set intervals.

Must my child stay in the hospital between the scan and the blood samples?

Your child can leave the hospital between the scan and the blood samples, but they must return at the time(s) given by the technologist.

When are the results available?

A nuclear medicine doctor will send a report to your family doctor or paediatrician (child's doctor) within one or two working days of the test. Please contact your family doctor to get the results. You will not be able to get the results from the nuclear medicine technologist.

At SickKids

If your child needs a blood test before the renal scan and GFR, it can be done in the Ambulatory Centre on the main floor near Shoppers Drug Mart. Please arrive at the hospital early to allow enough time for the test and be on time for the scan.

If you have any questions or concerns about the test or if you need to change your appointment, please call the Nuclear Medicine Department at 416-813-6065.