About Kidney Function

Glomerular Filtration Rate (GFR) Based on Creatinine Measurement

Glomerular Filtration Rate (GFR) is a calculation of how efficiently the kidneys are able to filter wastes from the blood. One way of determining GFR requires the injection of a substance into the bloodstream that is later measured in the urine which is collected for a 24-hour period. However, scientists found they could calculate GFR with less trouble, without an injection or a 24-hour urine collection. The calculation -- called the eGFR -- requires a measurement of creatinine in a blood sample. (The “e” in eGFR stands for “estimated”)

In a laboratory, a person's blood is tested to see how much creatinine is in the blood. Creatinine levels in the blood can vary, and each laboratory has its own normal range. A person whose creatinine level is only slightly above this range will probably not feel sick, but the elevation is a sign that the kidneys are not working at full strength. But because creatinine values differ so much from person to person and can be affected by diet, a GFR calculation is more accurate for determining whether a person has reduced kidney function.

The eGFR calculation uses the patient's creatinine measurement along with age and values assigned for gender and race. Some medical laboratories may make the eGFR calculation when a creatinine value is measured and include it on the lab report. The different stages or severity of Chronic Kidney Disease (CKD) are based on the value of the eGFR. Dialysis or transplantation is needed when the eGFR is less than 15 milliliters per minute (mL/min).

(Adapted from National Kidney and Urologic Diseases Information Clearinghouse [NKUDIC]: The Kidneys and How They Work)