MedlinePlus defines a GFR level as the rate at which the kidneys filter waste from the blood. GFR is an acronym for glomerular filtration rate, and the measurement is an indicator of how healthy the kidneys are.
MedlinePlus indicates that a doctor orders a blood test for GFR levels when a patient exhibits symptoms of poor kidney function, or to determine the progression of kidney disease. Age, gender, weight, height, ethnicity and the level of creatinine in the blood influence GFR and are taken into account by the lab professional who performs the test. Normal GFR levels fall between 90 to 120 milliliters per minute per 1.73 square meters.