Clarifying the concept of chronic kidney disease for non-nephrologists

Abstract

Chronic kidney disease (CKD) expands the prior concept of chronic renal insufficiency by including patients with relatively preserved renal function, as assessed by the estimated glomerular filtration rate (eGFR), as even these early CKD stages are associated with an increased risk for all-cause death and cardiovascular death, CKD progression and acute kidney injury. A decreased eGFR (<60 mL/min/1.73 m²) is by itself diagnostic of CKD when persisting for >3 months. However, when eGFR is ≥60 mL/min/1.73 m², an additional criterion is required to diagnose CKD. In a recent clinical trial published in The New England Journal of Medicine, all 6190 participants were reported to have CKD: 47% had Stages 1 and 2 CKD and 53% had Stage 3 CKD. This illustrates a widespread misunderstanding of the concept of CKD. Moreover, CKD categories in this study were assigned based on the estimated creatinine clearance. Since both estimated creatinine clearance and creatinine clearance overestimate eGFR, this illustrates another frequent misunderstanding: equating GFR with creatinine clearance. In this commentary, we clarify the concept of CKD and of CKD categories for non-nephrologists. Assigning a diagnosis of CKD to a patient with normal renal function and absence of other evidence of CKD may have negative consequences for the individual (e.g. insurance and others) as well as for the medical community at large by creating confusion about the concept.

Keywords: albuminuria; chronic kidney disease; creatinine clearance; definition; glomerular filtration rate; urate.

FIGURE 1

Heatmap representing the risk for CKD progression according to GFR and albuminuria categories [1]. Similar heatmaps represent the risk for all-cause death and cardiovascular death.

FIGURE 2

Data presented in Table 1 of the recent 2018 NEJM manuscript by White et al. [5]. All 6190 participants were reported to have CKD. Patients were randomized to either febuxostat (N = 3098) or allopurinol (N = 3092). The table legend stated that ‘estimated creatinine clearance was calculated with the use of the Cockcroft–Gault formula and was corrected for ideal body weight. A value of 60 mL per minute or more indicated Stage 1 or 2 chronic kidney disease, and a value of at least 30 but less than 60 mL per minute indicated Stage 3 chronic kidney disease’. However, no other evidence of CKD (e.g. such as pathological albuminuria in those with creatinine clearance >60 mL/min) was provided. Indeed, albuminuria data were not available [11].