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Glomerular Filtration Rate (GFR) Test

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What is a glomerular filtration rate (GFR) test?

A glomerular filtration rate (GFR) is a blood test that checks how well your kidneys are working. Your kidneys have tiny filters called glomeruli. These filters help remove waste and excess fluid from the blood. A GFR test estimates how much blood passes through these filters each minute.

A GFR can be measured directly, but it is a complicated test, requiring specialized providers. So GFR is most often estimated using a test called an estimated GFR or eGFR. To get an estimate, your provider will use a method known as a GFR calculator. A GFR calculator is a type of mathematical formula that estimates the rate of filtration using some or all of the following information about you:

  • The results of a blood test that measures creatinine, a waste product filtered by the kidneys
  • Age
  • Weight
  • Height
  • Gender
  • Race

The eGFR is a simple test that can provide very accurate results.

Other names: estimated GFR, eGFR, calculated glomerular filtration rate, cGFR

What is it used for?

A GFR test is used to help diagnose kidney disease at an early stage when it is most treatable. GFR may also be used to monitor people with chronic kidney disease (CKD) or other conditions that cause kidney damage. These include diabetes and high blood pressure.

Why do I need a GFR test?

Early stage kidney disease doesn’t usually cause symptoms. But you may need a GFR test if you are at higher risk of getting kidney disease. Risk factors include:

  • Diabetes
  • High blood pressure
  • Family history of kidney failure

Later stage kidney disease does cause symptoms. So you may need a GFR test if you have any of the following symptoms:

  • Urinating more or less often than usual
  • Itching
  • Fatigue
  • Swelling in your arms, legs, or feet
  • Muscle cramps
  • Nausea and vomiting
  • Loss of appetite
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What happens during a GFR test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You may need to fast (not eat or drink) or avoid certain foods for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk of having a blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your GFR results may show one of the following:

  • Normal—you probably don’t have kidney disease
  • Below normal—you may have kidney disease
  • Far below normal—you may have kidney failure

If you have questions about your results, talk to your health care provider.

Is there anything else I need to know about a GFR test?

Although damage to kidneys is usually permanent, you can take steps to prevent further damage. Steps may include:

  • Blood pressure medicines
  • Medicines to control blood sugar if you have diabetes
  • Lifestyle changes such as getting more exercise and maintaining a healthy weight
  • Limiting alcohol
  • Quitting smoking

If you treat kidney disease early, you may be able to prevent kidney failure. The only treatment options for kidney failure are dialysis or kidney transplant.

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References

  1. American Kidney Fund [Internet]. Rockville (MD): American Kidney Fund, Inc.; c2019. Chronic Kidney Disease (CKD) [cited 2019 Apr 10]; [about 2 screens], Available from: http://www.kidneyfund.org/kidney-disease/chronic-kidney-disease-ckd
  2. Johns Hopkins Medicine [Internet]. Baltimore: The Johns Hopkins University; c2019. Chronic Kidney Disease [cited 2019 Apr 10]; [about 3 screens]. Available from: https://www.hopkinsmedicine.org/health/conditions-and-diseases/chronic-kidney-disease
  3. Lab Tests Online [Internet]. Washington D.C.; American Association for Clinical Chemistry; c2001–2019. Estimated Glomerular Filtration Rate (eGFR) [updated 2018 Dec 19; cited 2019 Apr 10]; [about 2 screens]. Available from: https://labtestsonline.org/tests/estimated-glomerular-filtration-rate-egfr
  4. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [cited 2019 Apr 10]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  5. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Chronic Kidney Disease Tests and Diagnosis; 2016 Oct [cited 2019 Apr 10]; [about 4 screens]. Available from: https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis
  6. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Frequently Asked Questions: eGFR [cited 2019 Apr 10]; [about 5 screens]. Available from: https://www.niddk.nih.gov/health-information/communication-programs/nkdep/laboratory-evaluation/frequently-asked-questions
  7. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Glomerular Filtration Rate (GFR) Calculators [cited 2019 Apr 10]; [about 5 screens]. Available from: https://www.niddk.nih.gov/health-information/communication-programs/nkdep/laboratory-evaluation/glomerular-filtration-rate-calculators
  8. National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2019. A to Z Health Guide: About Chronic Kidney Disease [cited 2019 Apr 10]; [about 3 screens]. Available from: https://www.kidney.org/atoz/content/about-chronic-kidney-disease
  9. National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2019. A to Z Health Guide: Estimated Glomerular Filtration Rate (eGFR) [cited 2019 Apr 10]; [about 3 screens]. Available from: https://www.kidney.org/atoz/content/gfr
  10. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida; c2019. Glomerular filtration rate: Overview [updated 2019 Apr 10; cited 2019 Apr 10]; [about 2 screens]. Available from: https://ufhealth.org/glomerular-filtration-rate
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2019. Health Encyclopedia: Glomerular Filtration Rate [cited 2019 Apr 10]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=glomerular_filtration_rate
  12. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Glomerular Filtration Rate (GFR): Topic Overview [updated 2018 Mar 15; cited 2019 Apr 10]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/special/glomerular-filtration-rate/aa154102.html
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