Renal Clearance

The glomerular filtration rate is an effective metric for assessing kidney function. One way of measuring GFR is by calculating renal clearance.

Renal clearance measures the volume of blood plasma cleared of a particular substance, like creatinine, per unit of time.   

Over a 24-hour period, urine samples are collected at every bladder voiding, followed by a blood sample at the end of the interval.

Renal clearance is then calculated as the product of the substance concentration in urine and the urine flow rate divided by its plasma concentration. It is usually measured in milliliters per minute.

High renal clearance indicates that most of the substance is filtered out for excretion, while low clearance implies it is reabsorbed into the bloodstream.

For example, blood glucose under normal levels is completely reabsorbed and not excreted, so glucose clearance is usually zero in healthy individuals.

For a substance that gets completely filtered and not reabsorbed or secreted, renal clearance will equal GFR.

Inulin, a plant polysaccharide, is a standard substance with high renal clearance. It is commonly used to measure GFR accurately.