Glomerular Filtration Rate Test (GFR) – Why am I having this test?
Glomerular filtration rate is a measurement of how well your kidneys are functioning. You may have this test to diagnose or assess the severity (stage) of kidney disease.
This test is sometimes also called a calculated, or estimated, glomerular filtration rate (eGFR).
What is being tested?
Your GFR is estimated or calculated based on your:
- Creatinine level in your blood. Creatinine is a waste product from your muscles. Healthy kidneys filter creatinine out of your blood.
- Age.
- Gender.
- Race.
- Height.
- Weight.
What kind of sample is taken?
A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel.
Tell a health care provider about:
- All medicines you are taking, including vitamins, herbs, eye drops, creams, and over-the-counter medicines.
- Whether you are pregnant or may be pregnant.
How are the results reported?
Your results will be reported as milliliters of creatinine per minute (mL/min). Your health care provider will compare your results to a normal range that was established after testing a large group of people (reference range). Reference ranges may vary among labs and hospitals. For this test, a common reference range is 90–120 mL/min.
What do the results mean?
A result within the reference range is considered normal, meaning that your kidneys are filtering creatinine from your blood normally. A GFR below 60 mL/min for 3 months or longer is a sign of long-term (chronic) kidney disease. You may also have other tests to help your health care provider diagnose kidney disease. These tests may include:
- Urine tests.
- Removal and examination of a piece of kidney tissue (biopsy).
- Imaging tests such as an ultrasound, X-ray, or MRI.
If you are diagnosed with kidney disease, your GFR can also indicate your stage of kidney disease:
- GFR of 60–89 mL/min means mild kidney disease (stage 2).
- GFR of 30–59 mL/min indicates moderate kidney disease (stage 3).
- GFR of 15–29 mL/min indicates severe kidney disease (stage 4).
- GFR of less than 15 mL/min indicates kidney failure (stage 5).
Talk with your health care provider about what your results mean.
Questions to ask your health care provider
Ask your health care provider, or the department that is doing the test:
- When will my results be ready?
- How will I get my results?
- What are my treatment options?
- What other tests do I need?
- What are my next steps?
Summary
- Glomerular filtration rate (GFR) is a measurement of how well your kidneys are functioning. You may have this test to diagnose or assess the stage of kidney disease.
- Your GFR is estimated or calculated based on the creatinine level in your blood and several other factors, such as age, gender, race, height, and weight.
- A GFR below 60 for 3 months or longer is a sign of chronic kidney disease. You may also have other tests to help your health care provider diagnose kidney disease.
