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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.
A GFR test may be done to measure kidney function before, during or after chemotherapy.
GFR is usually tested as an outpatient procedure in the nuclear medicine department of a hospital. No special preparation is usually needed.
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.
A radiopharmaceutical is injected into a vein in the hand or arm. Technetium-99m (Tc-99m) is usually the radiopharmaceutical used.
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.
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:
A GFR study can detect problems in kidney function.
The doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed.
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.
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:
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.