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.<ref name="ZalupsLash1996">Template:Cite book</ref><ref name="Khurana2005">Template:Cite book</ref> It is defined by following equation:

<math> clearance\ ratio\ of\ X = \frac{C_x}{C_{in}}</math>

• 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.<ref>Template:Cite journal</ref> 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.

See also

• Clearance (pharmacology)
• Kt/V