What is the GFR on a blood test?

The GFR, or glomerular filtration rate, indicates how well the kidneys are filtering waste from the blood, states MedlinePlus. GFR is calculated using a formula that includes age, creatinine level, ethnicity, gender, height and weight. A normal GFR ranges from 90 to 120 milliliters per minute per 1.73 square meters.

Doctors suspect chronic kidney disease if a patient's GFR is less than 60 for 3 months or more, according to MedlinePlus. A GFR less than 15 usually indicates kidney failure and requires prompt medical care. Patients should inform their doctor if they are pregnant, or taking antibiotics or medications to control stomach acid, because these factors can affect GFR.