Did Creatinine Standardization Give Benefits to the Evaluation of Glomerular Filtration Rate?

During the last decade, a lot of efforts has been made to improve the evaluation of renal functions. Measured Glomerular Filtration Rate (GFR) remains the only valuable test to confirm or confute the status of chronic kidney disease (CKD) and is recommended by Kidney Disease Global Outcomes guidelines when estimation of GFR is not reliable. However, in routine clinical practice, serum creatinine remains the one of the most prescribed biological parameters and is an undeniable factor, alone or in association with other parameters, of the estimation of GFR. Since many years, a great improvement in the creatinine measurements was realized because of the standardization of the methods and fabrication of an international standard with concentration near to physiological ones (SRM967). Standardization according to Isotopic Dilution Mass Spectrometry dramatically improves the analytical performances of creatinine assays resulting in a more accurate estimation of GFR using creatinine based equations. Indeed, the standardization of creatinine improves the analytical performance by reducing the bias and removing the influence of the interfering substances. However, biological variability of creatinine is not affected by analytical standardization and remains a limitation to the use of creatinine in some selected populations, having extreme ages or weights like children, elderly subjects, obese or malnourished populations. Standardization of creatinine assays result in a clear improvement of estimated GFR in general population but alternative methods should be used when creatinine production or metabolism is impaired.