GFR (Glomerular Filtration Rate) Study Factsheet
Introduction
The kidneys help remove waste and extra fluids from the blood, turning them into urine. A Globular filtration rate (GFR) study checks how well your child’s kidneys work by measuring how much blood the kidneys filter every minute.
In a GFR study, a special substance called radiotracer is injected into the body. Radiotracer is a small amount of radioactive fluid that travels through the blood and is filtered by the kidneys.
Your child will have several blood tests to see how much radiotracer is still in their blood. The amount of radiotracer left in the blood helps doctors calculate the GFR, which can tell them how well the kidneys are working.
The GFR study can be used to check:
- how well the kidneys are working
- kidney problems caused by chemotherapy or other drugs that can harm the kidneys
- kidney function in children with kidney disease
- kidney function before surgery
- how well one kidney is working on its own.
Before the test
Your child can eat and drink normally before the scan. Your child will be weighed to help calculate the correct amount of radiotracer.
The risks of radiation and allergic reactions are very low. Let your child’s treatment team know if they have any allergies.
Talk to your child's doctor or treatment team if you have any concerns or questions.
Numbing cream
Needles can be uncomfortable for children. Numbing cream can be used on children over two years old.
If your child needs numbing cream, you will need to:
- ask for it before the day of the scan
- arrive 30 minutes early to the appointment so it has time to work.
During the test
The GFR study has four parts and will take about 4.5 hours in total. You can stay with your child during the test.
There are long gaps between each blood test; however, you do not need to remain in the department.
Part 1
- your child will receive a small injection of radiotracer into their vein using a thin butterfly needle
- after the injection, your child will need to wait for two hours.
Part 2
- after two hours, your child will return for a blood test
- if your child has a Central Venous Access Device (CVAD), it can be used to take the blood.
- your child will then need to wait for one hour.
Part 3
- your child will return for another blood test
- if your child has a CVAD, it can be used to take the blood.
- your child will then need to wait for one hour.
Part 4
- your child will return for the final blood test
- if your child has a CVAD, it can be used to take the blood.
- your child can leave after this final test.
After the test
You can leave once the last blood sample has been collected.
The results will be sent to your child’s doctor within a couple of days. You will need to schedule a follow-up appointment with your child’s doctor to discuss the results.
Management
Radiation
Your child will be exposed to a small amount of radiation during the test. The benefits of finding and treating kidney problems are greater than the small risk of this low dose.
Allergic reactions
Allergic reactions to radiotracer are very rare and usually mild. Your child’s doctor will talk to you about any potential risks before the test. Let your child’s treatment team know if they have any allergies.
Supporting your child during the scan
Blood tests can be stressful for children. You can help by:
- explaining why the test is needed and how it works in simple words
- bringing comfort items like a blanket, toy, or dummy
- asking the treatment team about support from Child Life Therapy services
- arriving 30 minutes early if using numbing cream for the injection.
