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What Is Glomerular Filtration Rate (GFR)?

Reviewed by: HU Medical Review Board | Last reviewed: December 2022

The glomerular filtration rate (GFR) is an estimation of how well your kidneys are working. The GFR test is one of the main tests used to help diagnose chronic kidney disease (CKD). The GFR can also help doctors detect which stage your kidney disease is in.1,2

Why is the GFR important?

Each kidney is made up of millions of tiny filtering units called nephrons. Each nephron is made up of a glomerulus and a tubule.3

The heart pumps blood into your kidneys. The glomeruli then filter your blood of any extra waste while the tubules return nutrients back to your blood and remove the waste. The waste then leaves your body when you pee. The GFR test tells how well your kidneys perform these jobs.3

How does the GFR work?

First, your doctor collects a blood sample. They then analyze it to find out how much creatinine is in your blood.1,2

Creatinine is a waste product in your blood that is produced with normal wear and tear of your muscles. Healthy kidneys filter creatinine out of your blood and release it in pee. But if your kidneys are not working well, creatinine builds up in your blood.1,2

Your doctor estimates your GFR number based on several pieces of information. They take into account:1,2

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  • The creatinine levels in your blood
  • Your age
  • Your sex
  • Your weight
  • Your height

Ask your doctor what you need to do to prepare for the GFR test.2

What does my GFR number mean?

The GFR test gives you a number that represents your kidney function level. A normal GFR is 60 or higher. The lower your GFR number, the more damaged your kidneys are and the more you are at risk of developing CKD.1

Here are the stages of kidney disease, along with their matching GFR levels:1

  • Stage 1 (kidney damage with normal kidney function) – 90 or higher GFR. This means you have 90 to 100 percent kidney function.
  • Stage 2 (mild loss of kidney function) – 89 to 60 GFR. This means you have 89 to 60 percent kidney function.
  • Stage 3a (mild to moderate loss of kidney function) – 59 to 45 GFR. This means you have 59 to 45 percent kidney function.
  • Stage 3b (moderate to severe loss of kidney function) – 44 to 30 GFR. This means you have 44 to 30 percent kidney function.
  • Stage 4 (severe loss of kidney function) – 29 to 15 GFR. This means you have 29 to 15 percent kidney function.
  • Stage 5 (kidney failure) – less than 15 GFR. This means you have less than 15 percent kidney function.

As you can see, you can still have kidney damage even when your GFR is within a “normal” range. If you have a waste product called albumin in your pee, that will also affect what stage of kidney disease your doctor assigns you.2,4

If you have a history of kidney disease or think you might have kidney damage, schedule an appointment with your doctor so they can check your levels.

Other tests may be needed

The GFR test is a reliable way for your doctor to diagnose you with kidney disease. But you may need other tests and imaging scans to give your healthcare team a clearer look at your kidneys and why you have kidney disease. These tests might include:1,2

  • Blood pressure test
  • Urine test to check for albumin in your pee
  • Ultrasound
  • Computed tomography (CT) scan
  • Kidney biopsy

Your GFR may change over time

As kidney disease progresses, your GFR number decreases. Early detection of kidney disease allows you to adopt healthy lifestyle habits that may help slow down how fast your GFR changes. These habits include following a kidney-friendly diet.1,2

It is normal for GFR to decrease as you get older. This is true even for people without kidney disease. It is also possible that your GFR may change over the course of your lifetime due to:1,2

  • Older age
  • Dehydration
  • Other medical conditions

Your kidney health

While you cannot reverse kidney damage, you can slow the progression of CKD by adopting healthy lifestyle habits. These habits include:1,2

  • Eating a low-salt diet
  • Controlling your blood sugar if you have diabetes
  • Controlling your blood pressure
  • Staying active
  • Not smoking

The sooner your kidney damage is discovered, the sooner you can get treatment. Talk with your doctor about having your GFR levels measured.1

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