Glomerular Filtration Rate (GFR) Test

Why this test may be ordered

• Screen for kidney disease in people without symptoms
• Help diagnose kidney disease in people who have symptoms
• Help find out how serious kidney disease is
• Monitor people with chronic kidney disease (CKD) to see if treatment is helping
• Check kidney health before people start certain treatments that could affect their kidneys

Preparation and collection

Your provider will let you know how to prepare. You may need to fast (not eat or drink) or avoid certain foods for several hours before the test. Certain medicines can affect your results, so tell your provider everything you're taking. Do not stop taking any medicine unless your provider tells you to stop.

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.

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

Understanding results

Your eGFR results may be reported as a number that shows how much blood your kidneys filter per minute. Your test results may also give your creatinine level and/or your cystatin C level. Ask your provider to explain what your eGFR says about your kidney health.

• Normal eGFR: You probably don't have kidney disease. Limitation: eGFR is an estimate and may not always reflect kidney damage. It's possible to have a normal result even if kidney damage is present. Next step: No immediate action needed. Continue routine monitoring as recommended by your provider.
• Below normal or low eGFR: You may have kidney disease. Limitation: eGFR is an estimate and may not always reflect kidney damage. It's possible to have an abnormal result without kidney damage. Next step: Your provider will explain what your eGFR means and may order additional tests such as a protein in urine test, microalbumin creatinine ratio, or BUN to check your kidney health.
• Very low eGFR: You may have kidney failure. Limitation: eGFR is an estimate and may not always reflect kidney damage. Other factors can affect the result. Next step: Your provider will explain steps to protect your kidneys from more damage and help prevent kidney failure. Additional tests and treatments may be needed.

• eGFR is an estimate and may not always reflect kidney damage.
• It's possible to have an abnormal result even if you don't have kidney damage.
• eGFR isn't a perfect test and may not always reflect kidney damage.

What to do next

If your eGFR is abnormal, your provider will explain what it means and may order additional tests such as a protein in urine test, microalbumin creatinine ratio, or BUN. If you are diagnosed with kidney disease, your provider will discuss steps to protect your kidneys and prevent further damage.

• What does my eGFR number mean for my kidney health?
• Do I need to fast or avoid any foods before the test?
• What medicines might affect my eGFR results?
• How often should I have this test if I have diabetes or high blood pressure?
• What other tests might I need to check my kidney function?

Evidence source

U.S. National Library of Medicine: Glomerular Filtration Rate (GFR) Test