Editorial Assessing renal function – searching for the perfect marker continues! Commentary on Markers of kidney function in the elderly in relation to the new CKD-EPI formula for estimation of glomerular filtration rate Jolanta Malyszko, Hanna Bachorzewska-Gajewska, Jacek Malyszko, Nomy Iaina-Levin, Grazyna Kobus, Slawomir Dobrzycki Arch Med Sci 2011; 7, 4: 658-664 Devaki R. Nair1, Shweta Mehta1, Dimitri P. Mikhailidis2 1Department of Clinical Biochemistry, Royal Free Hospital, London, UK 2Department of Clinical Biochemistry and Department of Surgery, Royal Free Campus, University College London Medical School, University College London (UCL), London, UK Submitted: 21 July 2011 Accepted: 13 August 2011 Arch Med Sci 2011; 7, 4: 565-567 DOI: 10.5114/aoms.2011.24120 Copyright © 2010 Termedia & Banach Serum creatinine, as a marker of renal function, continues to be used in spite of inaccuracies in its measurement as well as interference from other factors. This has resulted in a multitude of formulae for calculating the glomerular filtration rate (GFR). More recently, The National Kidney Foundation Dialysis Outcome Quality Initiative (K/DOQI) and the European Best Practice Guidelines recommended the use of the Modification of Diet in Renal Disease (MDRD) study population for reporting estimated GFR (eGFR) [1-3]. This is in preference to other formulae previously used to estimate renal function [4]. However, many of the shortcomings associated with eGFR calculation persist and the search for an ideal marker of renal function continues. The clearance of exogenous markers such as inulin (“gold standard” method) and synthetic poly fructose solutions as well as non-radioactive contrast media such as iohexol are considered as a more accurate evaluation of renal function [5]. Measurement of creatinine has suffered in the past from inter-laboratory differences, some of which are attributed to differences in calibration [6]. In addition, the measurement of creatinine by the most common method (Jaffé) is subject to interference by chromogens such as bilirubin, glucose and uric acid. Similarly, the enzymatic method is prone to interference by bilirubin and some antibiotics. Serum creatinine measurement is also influenced by factors such as creatinine turnover rate, tubular secretion of creatinine and creatinine production rate, which is reflected by the muscle mass [7]. Some studies have shown that administration of cimetidine to block tubular secretion improves the reliability of GFR measurement [8]. Some uniformity with measurement has been introduced by adoption of a common calibration to isotope dilution mass spectrophotometry standard with substantial improvement and traceability for creatinine measurements [9]. Larger muscle mass in Afro-Caribbeans and smaller muscle mass in South Asians would show variable renal function compared with renal function measured by gold standard methods if not corrected for muscle mass [7]. Corresponding author: Dr Devaki R. Nair BSc, MSc, MBBS, FRCPath Department of Clinical Biochemistry Royal Free Hospital Pond Street, London NW3 2QG, UK Phone: +44(0) 2077940500, ext. 35083 Fax: +44(0) 2078302235 E-mail: Devaki.Nair@nhs.net