Pediatric glomerular filtration (Glofil) rate (GFR) test

What is a pediatric glomerular filtration (Glofil) rate (GFR) test?

The kidneys contain glomeruli, tiny filters that remove waste from your blood. A GFR lab test measures how much blood the kidneys filter every minute. Glofil is a specific kind of GFR test. The test uses a tiny amount of a special radioactive medicine to measure kidney function.

Your child will have GFR kidney function testing in a comfortable area where our team makes sure you and your child have everything you need. The results help your child’s doctors understand how to plan the next steps for your child’s care.

What are the benefits of a pediatric glomerular filtration (Glofil) rate (GFR) test?

A glofil is a GFR test, which means it provides a clear, definite assessment of your child’s kidney function.

• Some kidney testing uses estimated glomerular filtration rate (eGFR). Because that test is an estimate, however, an eGFR test provides only a snapshot of kidney function.

• A glofil test is not an estimate. It tells your doctor exactly how your child’s kidneys are working.

Your child’s doctors use this information to make important decisions about your child’s care. Glofil results help your doctor determine precise dosages of medications for conditions such as kidney disease or cancer.

Your child may have glofil testing as part of their care for:

• Kidney (renal) disease

• Organ transplant, including kidney, liver, heart transplant as well as bone marrow transplant

• Cancer that requires chemotherapy

What are the side effects of a pediatric glomerular filtration (Glofil) rate (GFR) test?

A glofil test is very safe. It doesn’t have any known side effects.

What are the risks of a pediatric glomerular filtration (Glofil) rate (GFR) test?

The risk from a GFR test is extremely small. Your child might feel a little sore where the IV (intravenous line) goes into their skin.

What to expect with a pediatric glomerular filtration (Glofil) rate (GFR) test

We do glofil kidney function tests in our Nephrology department at Children’s Medical Center Dallas. The Glofil test takes a total of six to eight hours from start to finish, depending on your child’s needs and previous testing.

What to expect before a pediatric glomerular filtration (Glofil) rate (GFR) test

Before the glofil test, we give your child super-saturated potassium iodide (SSKI) drops. These drops protect your child's thyroid gland from the radioactive portion of the medicine we inject during the study.

For the glofil test, we place an IV catheter (a small tube) in your child’s hand, arm or foot. The IV lets us use just one needle poke for the whole day. If your child has a working peripherally inserted central catheter (PICC) or central line, we use that line instead of placing an IV.

What to expect during a pediatric glomerular filtration (Glofil) rate (GFR) test

The Glofil test starts in the morning with these steps:

• Blood test - We take a premedication blood sample. It won’t hurt – we take it through the IV.

• Medication - We inject a small amount of the Glofil test tracer through the IV. A nurse flushes (rinses) the IV with saline solution to keep it clear and make sure all the medicine enters your child’s bloodstream.

• Three blood samples - After the injection, we take three more blood samples, each five minutes apart.

After this first stage of the glofil testing, you and your child may leave the area for lunch or other appointments. Your care team will tell you when you need to come back – usually within four to six hours.

When you return, we take three more blood samples through the IV, 30 minutes apart. Then we carefully remove the IV and put a bandage on the puncture spot.

What to expect after a pediatric glomerular filtration (Glofil) rate (GFR) test

Your child doesn’t need to do anything special after the exam. They can return home and go back to their usual activities.

How do I prepare my child for a pediatric glomerular filtration (Glofil) rate (GFR) test?

Let your child know that you’ll need to spend the whole day (six to eight hours) at the hospital, but they will be having tests for only a small part of that time. Your child should wear comfortable clothes. You can bring along books, games, homework or whatever you and your child need and want for the day. You will stay with your child the whole time.

What is my child allowed to eat and drink before a pediatric glomerular filtration (Glofil) rate (GFR) test?

Your child can eat and drink as usual before a glofil test. It is very important that your child arrives well hydrated for the GFR kidney function test. Please give your child water before leaving home, upon arrival and throughout the day. Water is available in the testing area, or you may bring your own. Sports drinks and sodas are not recommended. Flavored water is ok. Hydration will greatly help with IV placement. It also helps prepare your child’s kidneys so we can measure their actual function.

In the know

What are the prep instructions for the pediatric glomerular filtration (Glofil) rate (GFR) test?

Please have your child drink plenty of water for several days before the test. Keep drinking water before you leave home, when you arrive at Children’s and throughout the day. Water is available in the testing area, or you may bring your own. Flavored water is ok to drink. We don’t recommend sports drinks, sodas or other sugary drinks.

If your child is receiving other medical care that could involve radiotracers, please note that your child should not have iodinated contrast media for 24 hours before the glofil exam.

What questions should I ask my provider about the pediatric glomerular filtration (Glofil) rate (GFR) test?

You may want to ask your provider:

• What will the glofil test tell us about my child’s condition and treatments?

• What medications should my child stop taking before the glofil test?

• Are there any potential aftereffects from glofil testing?

• How soon will we know if we need to make changes to my child’s care based on glofil test results?