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Glomerular Filtration Rate

Does this test have other names?

GFR, estimated glomerular filtration rate, EGFR

What is this test?

This is either a blood test or a urine test that looks for changes in how your kidneys function. Your kidneys have tiny filters called glomeruli. The filters help remove waste from your blood. Your glomerular filtration rate is the rate at which your blood is filtered each minute. A glomerular filtration rate can be estimated with great accuracy, based on your weight and age. This is called the estimated glomerular filtration rate, or EGFR.  

Why do I need this test?

You might have this test to see if your kidneys are working the way they should, especially if you have diabetes or high blood pressure. GFR can detect kidney disease in its earliest stages, when it is most treatable. GFR can also help figure out if you have a condition that causes decreased blood flow to the kidneys, such as congestive heart failure, shock, or dehydration – severe fluid loss. 

What other tests might I have along with this test?

Your doctor is likely to order other tests that measure kidney function and waste products, such as:

  • Blood creatinine

  • BUN, or blood urea nitrogen

  • Urine albumin 

What do my test results means?

A lab test result may be affected by many things, including the method the laboratory uses to do the test. If your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider. 

The normal range for GFR depends on your age, weight, and muscle mass. Here are typical ranges:

  • A GFR above 60 is considered normal.

  • A GFR below 60 may mean you have kidney disease.

  • A GFR of 15 or below means your kidneys could be failing.

If your test results indicate you have early kidney disease, your doctor may want to take steps to treat it aggressively.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. You may also need to collect a 24-hour urine sample.   

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. A urine test poses no known risks. 

What might affect my test results?

Your test results may be affected if you:

  • Exercised vigorously before testing

  • Are severely malnourished

  • Are severely overweight

  • Are taking certain drugs, including chemotherapies and kidney medications

  • Eat a lot of meat 

An incomplete urine specimen also can give false results.

How do I get ready for this test?

No special diet is required. But you should avoid eating meat or drinking tea or coffee the day of your test. Check with your doctor about taking any medications on testing day. And be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.

If you need to collect a 24-hour urine sample, be sure you understand how to do it.