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Glomerular filtration rate (GFR) study
A glomerular filtration rate (GFR) study is a test that uses radioactive materials or tracers (radiopharmaceuticals) and a computer to see how well the kidneys are working. Glomeruli are tiny filters in the kidney that remove waste products from the blood. The GFR refers to the amount of blood that is filtered per minute.
Why a GFR study is done
A GFR test may be done to measure kidney function before, during or after chemotherapy.
How a GFR study is done
GFR is usually tested as an outpatient procedure in the nuclear medicine department of a hospital. No special preparation is usually needed.
- It is important for a woman to tell the nuclear medicine staff if she is breast-feeding, pregnant or thinks she may be pregnant before having any nuclear medicine test.
- The person may be asked to wear clothing that has no metal zippers, belts or buttons. They may be asked to change into a gown during the test and remove glasses, jewellery or objects that could interfere with the test.
The GFR study has 2 stages: the radiopharmaceutical is given by injection (sometimes scans are done at this time), and then the person returns later for blood samples.
Giving the radiopharmaceutical
A radiopharmaceutical is injected into a vein in the hand or arm. Technetium-99m (Tc-99m) is usually the radiopharmaceutical used.
- Sometimes images are taken right after the injection.
- Giving the radiopharmaceutical usually takes 15 minutes.
Taking the blood samples
Blood samples will be taken at timed intervals, such as 2, 3 and 4 hours after the radiopharmaceutical is injected. A computer analyzes the samples to see how much TC-99m is in the blood.
After the study, the radioactive material quickly loses its radioactivity. It passes out of the body through the urine or stool (feces). Depending on the type of radiopharmaceutical used, it may take a few hours or days to completely pass out of the body.
- Drinking fluids after the procedure helps flush the radiopharmaceutical from the body.
- Instructions may be given for special precautions that need to be taken after urinating, such as to flush the toilet twice and to wash the hands thoroughly.
Potential side effects
The dose of x-rays or radioactive materials used in nuclear medicine imaging can vary widely. Dose depends on the type of procedure and body part being examined. In general, the dose of radiopharmaceutical given is small and people are exposed to low levels of radiation during the test. The potential health risks from radiation exposure are low compared with the potential benefits. There are no known long-term adverse effects from such low-dose exposure.
Some potential side effects that might occur include:
- Bleeding, soreness or swelling may develop at injection site.
- Allergic reactions to the radiopharmaceutical may occur, but are extremely rare.
What the results mean
A GFR study can detect problems in kidney function.
What happens if a change or abnormality is found
The doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed.
Special considerations for children
Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents and caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.
- Explain to children that when the radiopharmaceutical is given they will feel:
- a sharp prick when the needle is inserted
- slight pressure or tugging when the radiopharmaceutical is injected
Instructions may be given for special precautions that need to be taken when caring for children during the first 6–24 hours after the test:
- If the caregiver is pregnant, someone else should do most of the child care.
- Wear disposable, waterproof gloves when handling the child’s urine, stool or vomit, including diaper changes.
- Change sheets or clothing that has vomit, urine or stool smears on it.
- Wear disposable, waterproof gloves when handling sheets or clothing.
- Sheets and clothing can be washed in the regular laundry.
- Flush the toilet immediately after use by the child.
- Place diapers in the outside garbage.
The preparation for a GFR study depends on the age and experience of the child. Find out more age-specific information on helping children cope with tests and treatment.