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Defining acute kidney injury: what is the most appropriate metric?

Nature Clinical Practice Nephrology volume 4, pages 208–215 (2008)Cite this article

Abstract

Glomerular filtration rate (GFR) is the most widely accepted measure of kidney function. Acute kidney injury (AKI) is defined as a reduction in GFR. GFR is, however, rarely measured in clinical practice; instead, serum markers (primarily creatinine) are used to define AKI. Because serum creatinine level is not linearly related to GFR, the performance of this marker is associated with ascertainment bias and poor sensitivity. In this article we discuss the limitations and pitfalls of using serum markers to define AKI, and offer some suggestions for the future.

Key Points

  • Glomerular filtration rate (GFR)—the most widely accepted indicator of renal function—is rarely measured directly in clinical practice; instead, it is estimated using equations for which serum markers (e.g. creatinine level) are variables

  • Even when measured directly, GFR does not indicate the function of renal tubules, which are nearly always damaged during acute kidney injury (AKI)

  • In patients with AKI, serum creatinine levels often do not increase until injury is severe; a lack of standard definitions of AKI also hampers optimization of outcomes and comparison of data from different trials

  • Trials in AKI should report relative rather than absolute serum creatinine levels, use 'hard' primary outcomes (e.g. need for dialysis), and validate emerging biomarkers of renal injury

  • It seems most likely that kidney function will eventually be assessed using a set of serum biomarkers, whereas kidney injury will be detected and followed up primarily using a set of urinary biomarkers

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Figure 1: Hypothetical relationship between two definitions of acute kidney injury.

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Authors and Affiliations

  1. in the Division of Nephrology and Hypertension, R Solomon is Professor of Medicine and Director, and A Segal is Associate Professor, Fletcher Allen Health Care at the University of Vermont College of Medicine, VT, USA.,

    Richard Solomon & Alan Segal

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  1. Richard Solomon
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  2. Alan Segal
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Correspondence to Richard Solomon.

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The authors declare no competing financial interests.

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Solomon, R., Segal, A. Defining acute kidney injury: what is the most appropriate metric?. Nat Rev Nephrol 4, 208–215 (2008). https://doi.org/10.1038/ncpneph0746

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