Renal clearance ratio

Diagram showing the basic physiologic mechanisms of the kidney

The renal clearance ratio or fractional excretion is a relative measure of the speed at which a constituent of urine passes through the kidneys. It is defined by following equation:

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

• X is the analyte substance
• C_x is the renal plasma clearance of X
• C_in is the renal plasma clearance of inulin.

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. 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.

See also

• Clearance (pharmacology)
• Kt/V