Renal clearance

Renal clearance is the volume of blood plasma from which the kidneys completely remove a substance per unit time. It quantifies kidney handling of that substance, not the amount of urine produced.

Clearance equation: A relation defining clearance as urinary excretion rate divided by plasma concentration. This equation turns urine concentration and flow into the plasma volume cleared per time.
Inulin clearance: A measurement of inulin excretion relative to its plasma concentration. Inulin is filtered but neither reabsorbed nor secreted, making its clearance an estimate of filtration rate.
Renal physiology: The study of kidney structure and function, including filtration, tubular transport, and urine formation. Clearance summarizes several renal processes in a single measurable quantity.
Glomerular filtration rate measurement: The estimation of plasma volume filtered by the glomeruli per unit time. It measures filtration specifically; clearance can also reflect tubular secretion or reabsorption.
Glomerular filtration rate: The volume of plasma filtered through the kidney glomeruli per unit time. A freely filtered substance with no net tubular transport has clearance equal to this rate.
Creatinine clearance: An estimate of filtration rate calculated from urinary and plasma creatinine measurements. Creatinine is convenient to measure, though tubular secretion makes the estimate slightly high.
Glomerulus: A capillary tuft in a nephron where blood plasma is filtered into kidney tubules. The glomerulus determines how much of a substance enters the nephron by filtration.
Urinary excretion: The amount of a substance eliminated in urine over a specified interval. Excretion is an amount per time, whereas clearance is a plasma volume per time.
Tubular reabsorption: Movement of filtered substances from kidney tubule fluid back into the blood. Reabsorption lowers urinary excretion and therefore lowers clearance.
Para-aminohippurate clearance: A measure using para-aminohippurate excretion to estimate effective renal plasma flow. At low concentrations, filtration and strong secretion remove most para-aminohippurate in one kidney passage.

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