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How we estimate GFR - A pitfall of using a serum creatinine-based formula

Lookup NU author(s): Dr Shabbir Moochhala, Dr Suren Kanagasundaram


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Chronic kidney disease (CKD) is defined using the estimated glomerular filtration rate (eGFR). This has led to a large increase in the diagnosis of CKD in the United Kingdom, the majority of which is in its earlier stages and is detected in non-hospital settings. It is important to be aware that eGFR calculations will reflect inaccuracies in the measured serum creatinine, as the latter is an important component of the calculation. We report a case in which a patient with high muscle-mass who had consumed large quantities of a creatine-containing nutritional supplement presented with apparently reduced renal function on the basis of the serum creatinine and therefore also the eGFR calculation (MDRD equation). Creatine is an amino acid which is a precursor of creatinine, and is known to transiently increase serum creatinine. 6 weeks after discontinuing creatine ingestion, serum creatinine had fallen but still gave rise to an apparently abnormal calculated eGFR. In fact, renal function was shown to be normal when estimated using 24-hour urinary creatinine clearance. This case demonstrates that the upper extreme of muscle mass and ingestion of creatine can affect not only serum creatinine but also the calculated eGFR. Knowledge of common confounding factors and their effects on serum creatinine and eGFR will allow appreciation of the limitations of these measures of renal function, and can prevent unnecessary over-investigation of such patients. © 2007 Dustri-Verlag Dr. K. Feistle.

Publication metadata

Author(s): Refaie R, Moochhala SH, Kanagasundaram NS

Publication type: Article

Publication status: Published

Journal: Clinical Nephrology

Year: 2007

Volume: 68

Issue: 4

Pages: 235-237

Print publication date: 01/10/2007

ISSN (print): 0301-0430

ISSN (electronic):

Publisher: Dustri-Verlag Dr. Karl Feistle

PubMed id: 17969491