Before revision: 300px|Diagram showing the basic physiologic mechanisms of the kidney The renal clearance ratio or fractional excretion is a measure of the speed at which a constituent of urine passes through the kidneys.
After revision: relative300px|Diagram showing the basic physiologic mechanisms of the kidney The renal clearance ratio or fractional excretion is a measure of the speed at which a constituent of urine passes through the kidneys.