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Glomerular Filtration Rate (GFR)

What is a GFR?

A GFR is a test that measures the function of your kidneys. The glomeruli are tiny filters in your kidney that allow waste products to be removed from your blood. The rate refers to the amount of blood filtered per minute.

This test is done in the Nuclear Medicine department using special camera equipment. It is performed by giving your child a special dye, through a vein. This special dye is a clear liquid which travels through the bloodstream and allows us to see the kidneys. The camera detects invisible radiation coming from the special dye and creates the pictures. After the pictures, your child’s blood will be drawn at 1.5, 2, 2.5, and 3 hours after the special dye injection.

What should we do before the test?

You may keep your child’s routine eating, sleeping, and medicine schedules before the test. Your child’s doctor or a Children’s staff member may give you different instructions if your child will have sedation or more tests on the same day.

How is the test done?

A technologist will bring you and your child in to an exam room and explain the test to both of you.

The technologist will start an intravenous (IV) in your child’s vein, usually in the arm or hand. This involves a little poke, using a small IV needle. Once the IV is in place, the needle is removed and a tiny plastic tube stays in the vein. If your child has an implanted port-a-cath, Hickman, or Broviac, no IV is needed. The special dye is given into the IV and the pictures will start during this injection.

During the pictures, your child will lie still on an imaging table. A large camera will be positioned underneath the table. Nothing will be above your child when pictures are being taken. The camera does not make any loud noises. Pictures will take about 3 minutes. It is important that your child remain still during the pictures. If your child moves, the pictures will need to be redone.

After the scan your child will be free to leave. You will need to arrive in the clinic or inpatient unit shortly after the scan so blood draws can be done at 1.5, 2, 2.5, and 3 hours after the injection.

In between the scan and each blood draw your child may conduct normal activities.

After the last blood draw the test is complete.

Can I be with my child during the test?

You are welcome to stay with your child, even if you are nursing or pregnant. The test will take 4 hours, please plan accordingly. You and your child will spend 30 minutes in Nuclear Medicine; the remainder of the time will be in the Oncology clinic or inpatient unit.

What can I expect after the test?

Your child may go back to normal eating and activity after this test.

The small amount of special dye used for the test will leave your child’s body through their urine over the next 24-72 hours. You and your child will not notice any differences. Drinking plenty of water will help flush the Pentetate from your child’s body.

The blood test results are not available right away. You will receive results from the doctor who ordered the test.

How should I prepare my child?

Children are usually less afraid and feel more successful when they know what to expect and what is expected of them. You know your child best. The amount of detail you give will depend on your child’s age and developmental level, reactions to previous health care experiences, and degree of anxiety about this test. Talking about it can help your child be more comfortable with the test, which will make the test easier for both of you.

For many children, a big concern is whether or not the test will hurt. Assure them that there may be some discomfort which will only last a few moments. Remind them the test is important because it helps find out how their body is working inside.

Children and young adults of all ages may want to bring a comfort item, such as their own blanket and pillow. Younger children may also find it helpful to bring a favorite toy or pacifier. Older children and teens may want to bring an electronic device.

To learn more about preparing and helping your child cope with this test, call the child life department. Child life specialists are trained to help children understand and cope with medical producedures and can offer parents advice on how to talk with and support their child. There is no charge for child life services.

Child life department:
Children’s - Minneapolis (612) 813-6259


If you have questions or need more information about the test, call Children's radiology department at (612) 813-8200.

Last reviewed Hem/Onc 6/2015. ©Copyright

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This page is not specific to your child, but provides general information on the topic above. If you have any questions, please call your clinic. For more reading material about this and other health topics, please call or visit Children's Minnesota Family Resource Center library, or visit

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