Moderator's View: Should we diagnose CKD using the 'one-size fits all' KDIGO 2012 guideline or do we need a more complex age-specific classification system?

The KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease was published January 2013 [1]. Based on evidence provided by meta-analyses including >1.5 million subjects, this document proposed a new classification system for chronic kidney disease (CKD). This classification system is meant to be universal and is independent of age. Recently, Moynihan et al. [2] expressed strong concern in the BMJ series ‘Too much medicine’ about the harms of overdiagnosing CKD in low-risk elderly due to the use of a single eGFR threshold for all age groups. This leads to a brisk debate in the weeks thereafter showing very different views on this topic. We therefore invited two leading experts to debate the pros and cons of using age-specific cutoffs for diagnosing CKD. Conte, Minutolo and De Nicola present data showing that the relationship between GFR and morphological changes in the elderly is inconsistent. Reduced kidney function in this age group is the result of a mixture of physiological senescence, subclinical vascular disease and initial kidney structural changes which are difficult to separate from each other, thereby rendering the histopathological kidney function association less suited for defining kidney disease. They therefore focus on how to use the association between kidney measures and hard clinical outcomes like end-stage renal disease (ESRD) and death for diagnosing and classifying CKD. They describe how relative and absolute risk changes with age and draw parallels to traditional risk factors like blood pressure, cholesterol and glucose, which also have lower relative risks but higher absolute risks in the elderly. Still, nobody recommends age-specific thresholds for these risk factors today. Conte et al. argue that there is no reason to treat CKD different from other risk factors and conclude that the current thresholds defining CKD should not be changed in the elderly. Glassock has long advocated against the K/DOQI classification system for several reasons, but particularly its consequences for the elderly. In this elegant debate contribution he guides us through the potential problems with a definition using one threshold for all ages. He stresses the view that a decline in GFR is often a normal phenomenon associated with normal aging referring to cohorts with a substantial proportion of apparently healthy elderly having eGFR <60 mL/ min/1.73 m. There are also studies describing histological signs of nephrosclerosis in the majority of kidney donors aged 70–77 years. Proteinuria is highlighted as an essential finding of clinical relevant kidney disease leading to the dilemma whether the large group of elderly with GFR stage 3A and normal albuminuria has kidney disease or not. He also highlighted the fact that a 25% increased mortality risk (compared with eGFR 80 mL/min) is found at eGFR levels ranging from 74 mL/min/1.73 m in the youngest to 50 mL/min/1.73 m in those 75+ years. Glassock strongly concludes that a reduced GFR has different implications in different age groups, and the KDIGO guidelines should therefore be revised to include thresholds defining CKD that are age dependent. The current pro-con debate clearly shows that there is no universal agreement on CKD diagnosis and classification. However, national guidelines, hospitals and individual physicians need to decide on how to deal with this clinical problem. We would therefore like to add some general comments to broaden the previous discussion with the hope to facilitate the choice of how CKD should be diagnosed. First, is the term CKD a useful concept at all? Most kidney disease diagnosis is based on histopathological classifications which are often immature, complex and confusing with overlapping clinical features. This has seriously hampered kidney research and cooperation with non-nephrologists. Although P O L A R V IE W S IN N E P H R O L O G Y