Glomerular
filtration rate (GFR) is a test used to check how well the kidneys are
working. Specifically, it estimates how much blood passes through the
glomeruli each minute. Glomeruli are the tiny filters in the kidneys
that filter waste from the blood.
A blood sample is needed.
The
blood sample is sent to a lab. There, the creatinine level in the blood
sample is tested. The lab specialist combines your creatinine level
with several other factors to estimate your (GFR). Different formulas
are used for adults and children. The formula includes some or all of
the following:
- Age
- Blood creatinine measurement
- Ethnicity
- Gender
- Height
- Weight
The
creatinine clearance test, which involves a 24-hour urine collection,
can also provide an estimate of kidney function. But this method is not
always accurate.
Your
health care provider may ask you to temporarily stop any medicines that
may affect the test results. These include antibiotics and stomach acid
medicines.
Be sure to tell your provider about all the medicines you take. Do not stop taking any medicine before talking to your doctor.
Tell your doctor if you are pregnant or think you might be. GFR is affected by pregnancy.
When
the needle is inserted to draw blood, some people feel moderate pain.
Others feel only a prick or stinging sensation. Afterward, there might
be some throbbing or a slight bruise. These soon go away.
The
GFR test measures how well your kidneys are filtering the blood. Your
doctor may order this test if there are signs that your kidneys are not
working well. It may also be done to see how far kidney disease has
progressed.
The
GFR test is recommended for people with chronic kidney disease. It is
also recommended for persons who may get kidney disease due to:
- Diabetes
- Family history of kidney disease
- Frequent urinary tract infections
- Heart disease
- High blood pressure
- Urinary blockage
According to the National Kidney Foundation, normal results range from 90 - 120 mL/min/1.73 m2. Older people will have lower normal GFR levels, because GFR decreases with age.
Normal
value ranges may vary slightly among different laboratories. Some labs
use different measurements or test different samples. Talk to your
doctor about the meaning of your specific test results.
Levels below 60 mL/min/1.73 m2 for 3 or more months are a sign of chronic kidney disease. GFR result lower than 15 mL/min/1.73 m2 is a sign of kidney failure and requires immediate medical attention.
Veins
and arteries vary in size from one patient to another and from one side
of the body to the other. Obtaining a blood sample from some people may
be more difficult than from others.
Other risks associated with having blood drawn are slight, but can include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
GFR; Estimated GFR; eGFR
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