What is a glomerular filtration rate test?
A glomerular filtration rate test (GFR) is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood. The rate refers to the amount of blood that is filtered per minute.
A radiopharmaceutical called Technetium-99m DTPA is injected into one of your child's veins. Technetium-99m DTPA has a tiny amount of radioactive molecules in it.
After the injection, a 10-second picture of the injection site will be obtained. You will then be instructed to return to Nuclear Medicine for your child's blood to be drawn two, three, and four hours after the injection.
When might a GFR be needed?
The GFR allows the nuclear medicine physician to assess the degree of kidney impairment and to follow the course of kidney disease. However, the GFR provides no information on the cause of the kidney disease.
A GFR test can help measure kidney function in:
- patients who are undergoing chemotherapy
- patients who have had a renal transplant
- evaluation of renal donors
How should I prepare my child for a GFR?
No preparation is necessary. Keep in mind that this test requires a five-hour time commitment, so please plan your day accordingly.
- It is helpful to give your child a simple explanation as to why a GFR is needed, and assure him or her that you will be with him or her for the entire time.
- You may want to bring your child's favorite book, toy, or comfort object to use during waiting times.
What should I expect when I bring my child to the hospital for a GFR?
When you arrive, please go to the Nuclear Medicine check-in desk on the second floor of the main hospital. A clinical intake coordinator will check in your child and verify his or her registration information.
What happens during a GFR?
- You will be greeted by one of our nuclear medicine technologists, who will explain to you and your child what will happen during the study.
- A tiny amount of the radiopharmaceutical will be injected into one of your child's veins.
- A quick picture of the injection site will be taken to assure the success of the injection.
- After the injection your child will be free to leave. You will need to return to the department for blood draws at two, three, and four hours after the injection. The blood draws must be done from an extremity that was not used for the injection. The technologist will give you exact times to return for each blood draw. In between blood draws your child can conduct normal activities.
- If your child has a double lumen catheter, it can be used for the blood draws. If not, your child can either have an IV placed or have three individual veni-punctures for the blood draws.
- After the last blood draw, the examination is complete and you are free to leave.
Will my child feel anything during a GFR?
Your child may experience some discomfort associated with the insertion of the intravenous needle(s). The needle used for the procedure is small. Once the radiopharmaceutical is injected, the needle is withdrawn and a bandage is placed over the site of the injection. The area where the injection was given may be a little sore.
Is a GFR safe?
We are committed to ensuring that your child receives the smallest radiation dose needed to obtain the desired result.
- Nuclear medicine has been used on babies and children for more than 40 years with no known adverse effects from the low doses employed.
- The radiopharmaceutical contains a very tiny amount of radioactive molecules, but we believe that the benefit to your child's health outweighs potential radiation risk.
- The camera used to obtain the image does not produce any radiation.
- It is safe for you to be with your child the entire time if you are pregnant or nursing.
What happens after the GFR?
Once the study is complete, you and your child will be free to leave and resume normal activity.
How do I learn the results of the GFR?
The GFR study will be processed, and the nuclear medicine physician will provide a report to the doctor who ordered your child's GFR. Your child's doctor will then discuss the results with you.
How Boston Children's Hospital approaches GFRs
Our Nuclear Medicine and Molecular Imaging Program is committed to providing a safe, comfortable, and child-friendly atmosphere with:
- specialized nuclear medicine physicians with expertise in interpreting GFRs in children of all ages
- certified nuclear medicine technologists with years of experience imaging children and teens
- Child Life specialists to help families prior to and during exams
- equipment adapted for pediatric use, which means age-appropriate care for children
- protocols that keep radiation exposure as low as reasonably achievable while assuring high image quality.
To schedule an appointment at any of the Department of Radiology’s locations, please call 617-919-SCAN (7226).