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An epidemic of chronic kidney disease: fact or fiction?

The publication of the Kidney Disease Outcomes and Quality Initiative (KDOQI) clinical practice guidelines for the evaluation, classification and stratification of chronic kidney disease (CKD) in February of 2002 was a landmark event [1]. This effort has profoundly impacted clinical practice, helped bring some order to a chaotic system of nomenclature and stimulated a resurgence of interest in this longneglected domain of clinical nephrology [2]. The nephrology community is now using a definition of the five stages of CKD, based on the presence of ‘kidney damage’ and/or reduced estimated glomerular filtration rate (eGFR) for 3 months or more [1,3]. However, it is noteworthy that three of the five stages of CKD (stages 3, 4 and 5) were arbitrarily defined and based solely on the absolute threshold of eGFR (standardized to 1.73 m2 body surface area) without any requirement for concomitant evidence of ‘kidney damage’, such as proteinuria or adjustment for age and gender [2]. These levels of eGFR, combined with the similarly arbitrary selection of a time dimension (≥3 months) for their persistence to establish ‘chronicity’, became the ‘gold-standard’ for definition of a ‘disease’. The abbreviated modification of diet in renal disease (MDRD) equation for deriving an estimate of true glomerular filtration rate (GFR) from values of serum creatinine (calibrated to the standard used to derive the formula) quickly became the most widely used method for determination of eGFR, despite its lack of validation in subjects without CKD or across a wide spectrum of ages, body habitus, diet, ethnicity and geographic location [4]. Because of inaccuracies, relative to true GFR, when eGFR is >60 ml/min/1.73 m2 reporting of specific values of eGFR was recommended only when calculated values of <60 ml/min/1.73 m2 were obtained [5]. Despite