Glomerular Filtration Rate (GFR) Calculator

Glomerular filtration rate (GFR) is the measurement doctors use to find out how well your kidneys are working. Knowing your GFR score allows your doctor to determine the stage of your kidney disease and plan the most effective treatment.

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About The GFR Test

What Is GFR?

GFR measures the function of the glomeruli — tiny filters in your kidneys that remove waste from your blood. Your GFR results show how effectively your kidneys are working and how healthy they are overall.

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 plan and adjust your treatment.

How Do Doctors Calculate GFR?

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

The formula factors in your:

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

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

Your GFR Test Results

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 60-89 — A GFR of 60-89 may be normal for some people, such as the elderly or infants, if they don't have any kidney damage. A GFR of 60-89 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 of 30-59 can cause:
• Anemia.
• Early bone disease.
• High blood pressure.
• Stage 4: GFR of 15-29 — A person at stage 4 has severe CKD and a GFR of 15-29. 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 kidney transplant services to survive.

What Is A Normal GFR For My Age?

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 of:

• Below 60 for three months or more means you have kidney disease.
• 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 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.

Preparing For Your GFR Test

How Do I Prepare For My GFR Test?

Before the GFR blood test, you may need to:

• Avoid some foods, especially cooked meats, for 12 hours before the test.
• Fast (not eat or drink) the day of the test.
• Stop taking prescription or over-the-counter (OTC) drugs.

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

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, such as kidney stones and urinary tract infections.

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, wrists, and face.

The excess fluid can also contribute to:

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

Can I increase my GFR score?

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.
• Eat plenty of fruits and veggies.
• Exercise routinely.
• Follow a low-salt diet. Talk to your doctor about the DASH diet.
• Limit protein. Too much protein can strain the kidneys to get rid of protein waste.
• Maintain a healthy weight.
• Quit smoking.

How Can I Calculate My GFR?

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