Renal clearance ratio explained

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:

clearance ratio of X = (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 comparitor as creatinine is produced by the body, whereas inulin has to be intravenously infused.

See also

• Clearance (pharmacology)
• Kt/V

Notes and References

1. Book: Rudolfs K. Zalups. Lawrence H. Lash. Methods in Renal Toxicology. 1996. CRC Press. 978-1-4398-0560-2. 2–3.
2. Book: Khurana. Textbook Of Medical Physiology. 2005. Elsevier India. 978-81-8147-850-4. 561–2.
3. Christensen . Signe Engkjaer . Nissen . Peter H. . Vestergaard . Peter . Heickendorff . Lene . Brixen . Kim . Mosekilde . Leif . 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 . November 2008 . 69 . 5 . 713–720 . 10.1111/j.1365-2265.2008.03259.x.