Renal clearance ratio

The renal clearance ratio or fractional excretion is a relative measure of the speed at which a constituent of urine passes through the kidneys.

[1][2] It is defined by following equation: Creatinine is sometimes used instead of inulin as the reference substance; for example, the calcium-creatinine clearance ratio is used in an attempt to distinguish between different causes of a high plasma calcium concentration.

[3] It is easier to use creatinine rather than inulin as the comparitor as creatinine is produced by the body, whereas inulin has to be intravenously infused.