New definition of AKI: shifting the focus beyond mortality

To the editor,

We read with great interest the recent study [1] by Dr. Machado et al., which proposed a new definition for acute kidney injury (AKI) in critically Ill patients, based on varied urine output thresholds and time frames. This study uses in-hospital mortality as an outcome-oriented approach to compose the proposed UO-AKI classification, applying different time frames (3 h, 6 h, 12 h, and 24 h) and distinct cutoff points. Ultimately, the average UO over 6-h frame was used for the new classification, and AKI was redefined as follows: stage 1 (0.2–0.3 mL/kg/h), stage 2 (0.1–0.2 mL/kg/h), and stage 3 (< 0.1 mL/kg/h) over 6 h. this proposed classification demonstrated superior predictive accuracy over the KDIGO criteria, with improved NRI and IDI for mortality. However, some details need to be considered carefully when interpreting and applying the findings.

First, in the current study, the ability to predict death was used as a criterion to evaluate the quality of AKI criteria. However, the essence of the AKI definition is to reflect impaired excretion of metabolic waste due to damage to the renal tubules and/or renal interstitium. Moreover, not all AKI stages are associated with increased mortality. For instance, in a prospective study [2] including 4683 patients, Kaddourah et al. reported that severe AKI (stage 2–3) conferred an increased risk of death by day 28 after adjustment for 16 covariates while mild AKI stage 1 was not. Similarly, an analysis [3] of two large trials (COVID-19 Critical Care Consortium and LUNG-SAFE studies) showed that both 28-day and 90-day mortality risk was increased for patients with stage 2 (HR 2.00, p < 0.001) and stage 3 AKI (HR 1.95, p < 0.001), but not for stage 1. Therefore, using a mortality-oriented approach to define AKI may overlook the significance of mild AKI (stage 1) and may explain why the proposed classification's urine volume threshold for AKI stage 1 (0.2–0.3 mL/kg/h) is similar to the stage 3 threshold (0.3 mL/kg/h) in the KDIGO guidelines, albeit with different time frames. Also, this approach could introduce bias into the understanding of AKI’s clinical significance, as it focuses solely on the risk of death while neglecting the kidney dysfunction and injury that are essential to the definition of AKI. In addition, we are also somewhat unclear about the time frame definition. Were all time frames measured as the corresponding hours after ICU admission, or were they sliding windows? This distinction may be important for accurately defining AKI.

Finally, we commend Dr. Machado et al. for their significant work, and we hope our perspectives will help in the interpretation of these findings.

No datasets were generated or analysed during the current study.

1. Machado GD, Santos LL, Liborio AB. Redefining urine output thresholds for acute kidney injury criteria in critically Ill patients: a derivation and validation study. Crit Care. 2024;28(1):272.

   Article PubMed PubMed Central Google Scholar

2. Kaddourah A, Basu RK, Bagshaw SM, Goldstein SL, Investigators A. Epidemiology of acute kidney injury in critically Ill children and young adults. N Engl J Med. 2017;376(1):11–20.

   Article PubMed Google Scholar

3. McNicholas BA, Rezoagli E, Simpkin AJ, Khanna S, Suen JY, Yeung P, Brodie D, Li Bassi G, Pham T, Bellani G, et al. Epidemiology and outcomes of early-onset AKI in COVID-19-related ARDS in comparison with non-COVID-19-related ARDS: insights from two prospective global cohort studies. Crit Care. 2023;27(1):3.

   Article PubMed PubMed Central Google Scholar

Download references

Not applicable.

Authors and Affiliations

1. Department of Intensive Care, Zhejiang Hospital, 12# Linyin Road, No. 1229, Gudun Road, Hangzhou, 310013, Zhejiang, People’s Republic of China

   Lihong Zhu & Juan Lin

Authors

1. Lihong ZhuView author publications

   You can also search for this author in PubMed Google Scholar

2. Juan LinView author publications

   You can also search for this author in PubMed Google Scholar

Contributions

Lihong Zhu raised the question and Juan Lin wrote the letter. All authors have reviewed and approved the letter.

Corresponding author

Correspondence to Juan Lin.

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

Reprints and permissions

Cite this article

Zhu, L., Lin, J. New definition of AKI: shifting the focus beyond mortality. Crit Care 28, 379 (2024). https://doi.org/10.1186/s13054-024-05170-0

Download citation

• Received: 07 November 2024

• Accepted: 11 November 2024

• Published: 20 November 2024

• DOI: https://doi.org/10.1186/s13054-024-05170-0

Share this article

Anyone you share the following link with will be able to read this content:

Get shareable link

Sorry, a shareable link is not currently available for this article.

Copy to clipboard

Provided by the Springer Nature SharedIt content-sharing initiative