Glomerular Filtration Rate: What Is a GFR Test?

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What Is a GFR Test? 

A glomerular filtration rate (GFR) test can show your doctor if your kidneys are working correctly. A few common health conditions that can cause damage to your kidneys include high blood pressure, diabetes, and heart disease. Other less common medical conditions can also lead to kidney problems.Your GFR can be measured or estimated with a one-time blood test. The estimated GFR, or eGFR, is usually a part of regular blood tests that you get for your yearly physical exam. Read on for more information on GFR tests.

How Your Kidneys Work

You have two kidneys–one on each side of your body, near the bottom of your ribs. Your kidneys take waste products and extra water out of your blood. Your urine (pee) removes the unwanted materials from your body. If your body can’t get rid of these waste products, you can have many negative health effects. These include difficulty controlling your blood pressure and keeping your bones healthy.

Your kidneys have small filters, called glomeruli, that remove the things your body doesn’t need from your blood. The waste products get into your kidneys through blood vessels called arteries. Your kidneys separate the extra water and waste products from your blood and send them to your bladder to leave your body when you pee.

The GFR measures the amount of blood that travels through these filters every minute to show if your kidneys are working properly or if you have kidney damage.

How Is the Test Done And Who Should Take It?

The GFR test measures how well your kidneys work to eliminate waste products in your blood. The most accurate way to measure GFR is to do a timed test to see how long your kidneys take to clear a marker chemical. This test is expensive and not commonly done. Instead, your GFR is usually estimated using a one-time blood test. The GFR number or score is based on a test that measures a waste product called creatinine. 

One of the functions of your kidneys is to clear the blood of excess creatinine. Your muscles make creatinine while you move around doing regular activities every day. Creatinine produced by your tissues collects in blood vessels, where it’s carried away. If your kidneys aren’t working well, there will be more creatinine in your blood. 

Your doctor will look at the amount of creatinine in your blood to see if it’s normal for a person with your characteristics. They’ll put creatinine level and other information about you into a math formula that estimates your kidney function. The estimate is called a GFR test range.

Information that helps your doctor understand the GFR test range includes your:

  • Age
  • Height
  • Weight
  • Gender 
  • Race

Early kidney disease usually doesn’t cause symptoms. Often, your doctor will find GFR abnormalities when they ask for a creatinine test in blood panels done as part of your routine physical exams. Your doctor might decide to check your GFR if you have other health conditions or risk factors that can cause kidney damage. 

Risk factors for kidney disease include:

Damage to your kidneys can lead to chronic kidney disease (CKD) and kidney failure. Kidney disease can be prevented and slowed down if it’s diagnosed early.

How To Prepare Dor a GFR Test

Your doctor will tell you if you shouldn’t eat or drink before your GFR test. You should bring a list of medicines you take, including over-the-counter vitamins or supplements. Write down any questions that you have for the doctor as well.

Understanding Your GFR Test Results

Your GFR test results will show a number that can tell your doctor if your kidneys are not working normally and if you have kidney disease. Your GFR test results produce a number that scores or stages kidney disease. 

Higher stage numbers mean that your kidneys have more damage:

  • Stage 1: Normal, healthy kidneys
  • Stage 2: Early kidney disease
  • Stage 3: Moderate kidney disease
  • Stage 4: Severe kidney disease
  • Stage 5: Kidney failure

Normal GFR Results 

Normal GFR results in most adults are 90 or higher, but the cutoff number decreases in older adults. If you’re 60 or older, lower scores don’t mean you have kidney disease, because you lose some muscle when you get older. So, you won’t have as much creatinine in your blood. 

You can see the numbers for adults, by age group, in the list below:

  • 20-29 Years = 116 and up
  • 30-39 Years = 107 to 115
  • 40-49 Years = 99 to 106
  • 50-59 Years = 93 to 98
  • 60-69 Years = 85 to 92
  • 70 Years and Older = 75 to 84

If Your Test Is Abnormal, What’s Next?

You might have kidney disease if your GFR test results are not in the normal range. Your doctor will look at your results and the GFR score range to stage your kidney disease.

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For most adults, GFR results mean: 

  • Normal = 90 or higher
  • Early kidney disease = 60 to 89
  • Kidney disease = 15 to 59
  • Kidney failure = 0 to 14

Living With Kidney Disease

Kidney disease is a condition that can be treated and prevented from getting worse, which leads to kidney failure. If you have chronic kidney disease (CKD), there are some things you can do to stay as healthy as possible, including:

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  • Eating healthy foods that have less sugar and salt
  • Keeping your blood pressure, diabetes, and cholesterol controlled 
  • Not skipping appointments with your doctor or lab testing facility
  • If you smoke, stop smoking
  • Staying active by exercising and doing light activities, like walking for 30 minutes 5 times a week
  • Taking medications as directed by your doctor

When To Call Your Doctor

You should contact your doctor if you have risk factors for kidney disease. You should call your doctor if you have already been diagnosed with kidney disease and have these symptoms:

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  • Change in how often you have to pee
  • Blood or foam in pee
  • Feel like you need to throw up (nausea) or are throwing up (vomiting)
  • Trouble catching your breath and breathing while you do regular activities
  • Your skin feels very itchy and dry and has turned a darker color for no reason
  • Your hands and feet are swollen 
  • Feel extremely tired
  • Your muscles cramp or spasm (twitch)