Glomerular filtration rate
Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood.
How the Test is Performed
A blood sample is needed.
The blood sample is sent to a lab. There, the creatinine level in the blood sample is tested. Creatinine is a waste product from the digestion of dietary protein and the normal breakdown of muscle tissue.
The lab specialist combines your blood creatinine level with several other factors to estimate your GFR. Different formulas are used for adults and children. The formula includes some or all of the following:
- Age
- Blood creatinine measurement
- Ethnicity
- Sex
- Height
- Weight
Estimated Glomerular Filtration Rate
Your kidneys filter your blood by removing waste and extra water to make urine. The kidney’s filtration rate, called the glomerular filtration rate (GFR), shows how well the kidneys are filtering. An estimated 37 million adults in the United States may have chronic kidney disease (CKD) and can take the steps needed to protect their kidney function when it is found early.
GFR and eGFR
Testing for GFR can be a complicated and lengthy procedure, which is why doctors use a formula to estimate GFR or eGFR. Accurate estimates of the GFR are important for identifying kidney disease, which often has no symptoms until just before the kidneys fail. The standard way to estimate GFR is with a simple blood test that measures your creatinine levels. Aside from CKD, creatinine levels can be affected by other factors, including diet, muscle mass, malnutrition, and other chronic illnesses.
Why eGFR testing is done
Early stage kidney disease doesn’t usually cause symptoms, but your doctor may recommend a eGFR test if you are at higher risk of developing kidney disease. CKD risk factors include:
- Having diabetes or high blood pressure
- Being overweight
- Family history of kidney failure
Later stage CKD does cause symptoms. So you may need an eGFR test if you have any of the following symptoms:
- Urinating more or less often than usual
- Itching
- Feeling tired
- Swelling in your arms, legs, or feet
- Muscle cramps
- Nausea and vomiting
- Loss of appetite
What is a normal eGFR number?
In adults, the normal eGFR number is more than 90. eGFR declines with age, even in people without kidney disease. See chart below for average estimated eGFR based on age.
| Age (years) | Average eGFR |
| 20–29 | 116 |
| 30–39 | 107 |
| 40–49 | 99 |
| 50–59 | 93 |
| 60–69 | 85 |
| 70+ | 75 |
