Glomerular filtration rate (GFR) is a measure of how well the kidneys are filtering waste products from the blood. It specifically reflects the rate at which blood is filtered by the glomeruli, the tiny blood vessels in the kidneys that are responsible for filtering waste and excess fluid from the blood to produce urine.

GFR is considered one of the best indicators of kidney function. A GFR test estimates how much blood passes through the glomeruli each minute and is typically reported in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73 m²).

A normal GFR value can vary based on age, gender, body size, and ethnicity. However, in general:

• A GFR above 90 mL/min/1.73 m² is considered normal kidney function.
• A GFR between 60 and 89 mL/min/1.73 m² may indicate mild kidney damage or decreased kidney function.
• A GFR between 30 and 59 mL/min/1.73 m² may indicate moderate kidney damage or decreased kidney function.
• A GFR below 30 mL/min/1.73 m² may indicate severe kidney damage or decreased kidney function.

GFR is often estimated using mathematical equations that take into account factors such as serum creatinine level, age, gender, and race. Creatinine is a waste product generated by muscle metabolism that is filtered by the kidneys. A higher serum creatinine level generally indicates decreased kidney function.

GFR is an important parameter used in the diagnosis and monitoring of kidney diseases, such as chronic kidney disease (CKD). Monitoring changes in GFR over time can help assess kidney function and guide treatment decisions. Additionally, GFR is used to determine the stage of CKD, with lower GFR values corresponding to more advanced stages of the disease.