What is a Glomerular Filtration Rate (GFR) Study?
A glomerular filtration rate study is a test that shows how well the kidneys are working. A special medicine is injected into a vein and a few special pictures may be taken after a medicine is injected. If pictures are taken, we can compare how much each kidney is working.
Several blood samples are also taken starting 90 minutes after the medicine is injected. The blood samples measure how much of the medicine is still inside the blood. These blood samples will be taken with finger sticks or from a small needle that will be left in a vein during the study.
Before the Glomerular Filtration Rate Test
Before coming to the hospital, read this explanation and explain to your child what will happen during the test. For young children, use simple words and explain only shortly before the test.
If your child is an infant, it is helpful to bring along a bottle of formula or juice for after the test. It is also recommended that you bring a pacifier, blanket or special toy to help calm your child.
For older children, it is helpful to bring a book or toy to play with while waiting. It is helpful to have another caregiver watch your child's siblings during the test.
For children who receive TPN (Total Parenteral Nutrition), the TPN fluids need to be slowed down four hours before the glomerular filtration rate study, as TPN will change the test results. Ask your child's doctor when to slow down the TPN fluids.
During the Glomerular Filtration Rate Test
A technologist will place a small needle called an IV into your child's hand or foot. The needle stick hurts for just a moment. The medicine is then injected through the needle into the vein.
Special pictures may be taken for up to 9 minutes immediately after injection of the medicine. Your child will lie on a soft table while a camera takes pictures from below the child. If your child is unable to lie still, our staff will help your child hold still.
After injection of the medicine, and immediate pictures (if needed), there is a waiting period before the test continues. You may wait in the waiting area or go for a walk. You will be asked to return in 90 minutes. During this waiting period, your child may eat and drink, but it is important that he / she not eat or drink anything that contains caffeine, such as soft drinks, coffee, tea or chocolate.
When you return, blood samples will be taken three or four times, every 30 minutes. Your child will either have three or four finger sticks, or a small needle will be placed in his / her hand or foot and left in until all the blood samples are taken or a central line can be used. The line used to inject the medicine cannot be used to draw blood.
Between blood samples, you may wait in the waiting area or take a walk between the blood samples, but you must return at the scheduled times. The technologist will tell you when the test is complete.
After the Glomerular Filtration Rate Test
The medicine is removed from your child's body when he / she urinates. Your child should drink plenty of fluids and urinate often to help clear the medicine from his / her body.
The medicine should be completely out of your child's body within two days. As always, you and your child should wash your hands after the child urinates or when handling diapers or urine-soaked sheets.
After the test, your child may return to regular daily activities and meals. Results of the test will be sent to your child's doctor, who will contact you about the results.