Glomerular Filtration Rate

Does this test have other names?

GFR, estimated glomerular filtration rate, eGFR, calculated glomerular filtration rate, cGFR 

What is this test?

This is a blood 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 the result of other blood tests that measure serum creatinine and serum cystatin C. Other factors are used, such as your weight and age. This is called the estimated glomerular filtration rate, or eGFR.

GFR may be a urine test, but this is done only in special situations.

Why do I need this test?

You may need 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 heart failure, shock, or severe fluid loss (dehydration).

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:

• BUN, or blood urea nitrogen.

• Urinalysis.

• Urine albumin.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your doctor what your test results mean for you.

The normal range for GFR depends on your age, weight, and muscle mass. In most healthy people, the normal GFR is 90 or higher.

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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle has some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

What might affect my test results?

Your test results may be affected if you:

• Have changing kidney function.

• Are severely malnourished, are underweight, or have muscle-wasting disease.

• Are severely overweight.

• Are a bodybuilder.

• Have a neuromuscular disorder.

• Are taking certain medicines, including chemotherapies and kidney medicines.

• Eat a lot of meat.

• Eat a vegetarian or low-meat diet.

• Take creatine supplements.

• Are pregnant.

• Have health conditions that affect the kidneys.

How do I get ready for this test?

Usually, no special preparation is needed. Or you may need to make some changes to your diet. Check with your doctor about your diet and taking any medicines on testing day. 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 illegal drugs you may use.