The eGFR blood test isn’t actually a separate blood test. Lab personnel use data from other blood tests to determine an eGFR, or estimated glomerular filtration rate. This lab value allows doctors to determine how well the kidneys function.
Functions of the Kidneys
The kidneys carry out many essential functions in the human body. These functions include maintaining normal fluid levels, balancing electrolyte levels, producing urine, and filtering waste products out of the blood. The eGFR blood test allows doctors to determine how well the kidneys are carrying out their filtration functions. The result of this test helps doctors determine what other tests are needed to measure kidney function.
How eGFR Determined
Estimated glomerular filtration rate (eGFR) is calculated based on several factors, using one of several complicated formulas. The data needed to calculate glomerular filtration rate includes a person’s age, race, gender, and blood creatinine level. Creatinine forms during the breakdown of proteins in the human body. When the kidneys are functioning normally, they filter creatinine out of the blood and into the urine. The filtered creatinine leaves the body during urination. When kidney function declines, creatinine builds up in the blood, along with other waste products, leading to feelings of illness and malaise.
Lab technicians determine eGFR by performing a test known as the basic metabolic panel. During this test, a lab technician checks a blood sample to determine the levels of creatinine, sodium, blood urea nitrogen, glucose, potassium, chloride, and carbon dioxide in the blood. The laboratory computer now automatically calculates an estimated GFR using the creatinine result and information about the patient.
Normal glomerular filtration rate is above 90 ml/min, according to the National Kidney Foundation. Decreases in GFR indicate kidney problems. Doctors classify these problems in one of five stages.
- Stage one kidney disease: Normal GFR (above 90) with protein leakage from the kidneys
- Stage two kidney disease: GFR of 60 to 89
- Stage three kidney disease: GFR of 30 to 59
- Stage four kidney disease: GFR of 15 to 29
- Stage five kidney disease (end-stage renal failure): GFR of less than 15
When a person’s GFR drops below 15, doctors use hemodialysis to filter the blood mechanically, or they do a kidney transplant to replace the function of the failing kidneys. Patients with kidney failure only need one donor kidney, since one kidney can function well enough to maintain normal processes.
eGFR isn’t an exact indicator of kidney function since it is just an estimate. Doctors use the eGFR value, along with other test results, to determine how far kidney disease has progressed. The basic metabolic panel results also help doctors determine if the kidneys are unable to maintain normal electrolyte levels or maintain a proper acid-base balance in the blood. Diagnostic tests, such as renal ultrasound and CT scans (computerized tomography), also help reveal kidney problems. These tests show kidney cysts, tumors of the kidney, abnormal blood vessel function, urinary tract obstructions, and other conditions that could cause an abnormal glomerular filtration rate.