Therenal clearance ratio orfractional excretion is a relative measure of the speed at which a constituent ofurine passes through thekidneys.^[1][2] It is defined by following equation:

${\displaystyle clearanceratioofX=\frac{C_x}{C_{in}}}$

• X is theanalyte substance
• C_x is therenal plasma clearance of X
• C_in is the renal plasma clearance ofinulin.

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 comparator as creatinine is produced by the body, whereas inulin has to be intravenously infused.

• Clearance (pharmacology)
• Kt/V

• Nephrology