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Glomerular Filtration Rate (GFR) Calculator and FAQ

What Is GFR?

GFR is the measurement doctors use to find out your kidney function.

Knowing your GFR score lets your doctor learn the stage of your kidney disease and plan the best possible treatment.

Contact UPMC for Kidney Disease Care

Our kidney experts can work with you on a tailored treatment plan, taking into account your GFR and other factors.

To learn more or make an appointment at one of our clinics, call:

  • 412-802-3043.
  • 1-877-640-6746 (toll-free).
  • Physician referral line: 1-800-544-2500.

Try our GFR Calculator

Enter your age, serum creatinine, and gender to calculate your GFR.

How Do Doctors Compute GFR?

Your doctor will take a blood sample. Then they use a mathematical formula that estimates how well your kidneys are filtering waste.

You can't find out your GFR on your own because you need specific data from a blood test.

The formula includes the following:

  • Age.
  • Measurement of blood creatinine (a waste product filtered by the kidneys).
  • Ethnicity.
  • Sex.
  • Height.
  • Weight.

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Why Do I Need a GFR Test?

A GFR test is the most precise way of finding out how well your kidneys are working. It shows what stage of kidney disease you have.

Knowing your GFR and how it changes over time shows doctors how quickly your kidney disease is progressing. It will help them decide or adjust your treatment. 

What Is GFR in a Blood Test?

Glomeruli are tiny filters in the kidneys that strain waste from the blood. Damage to them can lead to kidney disease.

Doctors use blood test results in a formula that reveals how well the glomeruli in the kidneys are working.

Before the blood test, you may need to:

  • Stop taking prescription or over-the-counter (OTC) drugs.
  • Fast (not eat or drink).
  • Avoid some foods.

Your doctor will tell you how to prepare for the blood test.

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What Is a Normal GFR for My Age?

If you have kidney disease, you'll want to become familiar with your GFR.

For instance, you may wonder what a normal GFR is for a 70-year-old.

Your age is one of the main factors in determining GFR. GFR gets lower with age, even if you don't have kidney disease.

But no matter how old you are, a GFR:

  • Below 60 for three months or more means you have kidney disease.
  • Of 15 or below means you have end-stage kidney failure. You'll need dialysis or a kidney transplant to live.

What Does a Low GFR Mean?

A low GFR means your kidneys aren't filtering your blood as well as they should.

A GFR under 60 means you have kidney disease. If the number is below 15, you have kidney failure and will need dialysis or a kidney transplant.

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Can Dehydration Cause Low GFR?

Bouts of severe dehydration can sometimes lead to kidney injury and a lower GFR. But it isn't a typical cause of chronic kidney disease (CKD) and low GFR.

Chronic dehydration is more likely to lead to other problems, like kidney stones and urinary tract infections.

Check with your doctor about how much water you should drink each day.

If you have moderate to advanced kidney disease, you may need to limit fluid intake. Damaged kidneys can't filter as much fluid out of the body, causing swelling that leads to problems like high blood pressure.

Will Drinking Water Increase My GFR?

Increasing your water intake likely won't affect your GFR in the long run.

If your water intake is already at normal levels, drinking more won't slow your kidney disease. In fact, drinking too much water can be harmful.

If you have CKD, it's crucial to ask your doctor how much water you should drink. If you have moderate to advanced CKD, you may need to limit your water intake.

Damaged kidneys might not be able to remove extra fluid from the body, causing it to build up inside the body. This can cause swelling in your feet, ankles, wrist, and face.

The excess fluid can also contribute to:

  • Shortness of breath.
  • Heart problems.
  • High blood pressure.

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What Does My GFR Score Mean?

There are five stages of kidney disease. The lower your GFR score, the worse your kidney disease.

Stage 1 — GFR of 90+

A GFR of 90 or higher is normal in most healthy people. There are few (if any) symptoms at this stage of early CKD.

Stage 2 — GFR of 60 to 89

A GFR between 60 and 89 may be normal for some people — such as the elderly or infants. That's if they don't have any kidney damage.

A GFR between 60 and 89 for three months or longer along with kidney damage is a sign of early CKD. There are often few (if any) symptoms at this stage.

Stage 3 — GFR of 30 to 59

People at stage 3 have moderate CKD and may want to see a nephrologist.

A GFR between 30 to 59 can cause:

  • Anemia.
  • Early bone disease.
  • High blood pressure.

Stage 4 — GFR of 15 to 29

A person at stage 4 has severe CKD and a GFR between 15 to 29.

They will likely need dialysis or a kidney transplant in the future.

Stage 5—GFR of 15 or less

People with a GFR of 15 or less have end-stage renal disease (ESRD). The kidneys have lost almost all ability to function effectively.

People at stage 5 will need dialysis or a kidney transplant to survive.

Can I Improve My GFR?

You may be able to improve your GFR somewhat by changing your lifestyle.

Keep in mind that there's no cure for CKD. But healthy habits may slow the progression of the disease.

Because diabetes and high blood pressure are the main causes of CKD, it's vital to keep both under control.

Other ways to boost your kidney health are to:

  • Avoid processed foods, which are high in salt.
  • Follow a low-salt diet. Talk to your doctor about the DASH diet.
  • Eat plenty of fruits and veggies.
  • Limit protein. Too much protein can strain kidneys to get rid of protein waste.
  • Exercise routinely.
  • Cut back on or quit smoking.
  • Maintain a healthy weight.

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