Radionuclide GFR measures how fast the kidneys filter blood. The test is also called “plasma clearance”.
GFR stands for Glomerular Filtration Rate.
Normal GFR is 120 millilitres per minute. GFR may appear falsely low infants, breast-fed babies and children who are not well hydrated (for example because they have been fasting for a general anaesthetic).
A radionuclide GFR test may be done before the first cycle of chemotherapy as this is the most accurate way to assess kidney function.
Routine GFR scans are not recommended for children with known or suspected constitutional RB1 mutation as the radiation exposure increases risk of second cancers. They are usually used only before chemotherapy begins.
Before the Scan
GFR scans are done in the nuclear medicine or medical physics department. Your child will usually receive 3-4 hours of intravenous fluids before the scan.
An injection of isotope solution is then given before a gamma camera takes pictures to show blood supply and flow through each kidney.
Tell the doctor or radiographer if your child has asthma, because some people with asthma have a reaction to radionuclide. A pre-scan steroid may be prescribed to prevent a reaction, or an alternative test may be organized.
Your child may be asked to undress and put on a hospital gown. She will need to lie very still on the scanner bed.
Young children are often given a short acting general anaesthetic at this point, but with good child life support, children as young as 2 years can complete the scan awake.
If your child does not have a central line, an IV will be inserted to deliver the isotope solution. The injection may make her feel hot or flushed for a minute. This does not hurt, but she may cry if she is unprepared for this sensation.
During the Scan
This painless scan takes 10–20 minutes. Your child lies on the scan bed, with her head on a special pillow. The bed moves through the hole in the doughnut shaped machine so your child’s body is inside it.
During the scan, your child will be able to hear and speak to the technician through a microphone inside the scanner.
The radiographer leaves the room during the scan. Many hospitals allow parents to stay if the scan is done awake. You have the right to request this. Do advocate to stay with your child as your presence can be very reassuring. You will be asked to wear a lead apron to protect you from radiation exposure.
Some people feel claustrophobic inside the scanner, so prepare your child for this beforehand. You can often arrange a pre-scan visit with your child to familiarise yourselves with the machine.
After the Scan
If your child completes the scan awake, you will be free to go as soon as it is over.
If she has sedation or a general anaesthetic, you will usually be taken to recovery or a day care ward. You will be allowed to leave once she is fully awake and has had something to drink.
The body can take up-to 24 hours to completely remove all the radionuclide. Drinking plenty of fluids will speed up the process.
The radiographer or nurse will explain any precautions you need to take for the rest of the day, particularly if you have other young children. If you are unsure about what is expected or what the risks are, ask for clarification before leaving the hospital.
