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. ^{[1] [2]} It is defined by following equation:

${\displaystyle clearance\ ratio\ of\ X={\frac {C_{x}}{C_{in}}}}$

• 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. ^[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.

See also

• Clearance (pharmacology)
• Kt/V

References

1. Rudolfs K. Zalups; Lawrence H. Lash (1996). Methods in Renal Toxicology. CRC Press. pp. 2–3. ISBN   978-1-4398-0560-2.
2. Khurana (2005). Textbook Of Medical Physiology. Elsevier India. pp. 561–2. ISBN   978-81-8147-850-4.
3. Christensen, Signe Engkjaer; Nissen, Peter H.; Vestergaard, Peter; Heickendorff, Lene; Brixen, Kim; Mosekilde, Leif (November 2008). "Discriminative power of three indices of renal calcium excretion for the distinction between familial hypocalciuric hypercalcaemia and primary hyperparathyroidism: a follow-up study on methods". Clinical Endocrinology. 69 (5): 713–720. doi:10.1111/j.1365-2265.2008.03259.x.