Skip to main content

Validation of the AKIN criteria definition using high-resolution ICU data from the MIMIC-II database


Recently the Acute Kidney Injury (AKI) Network proposed criteria for the definition of AKI in the critically ill. The minimum hourly urine output rate used to define oliguria (< 0.5 ml/kg/hour) is based exclusively on clinical experience and animal models, not on clinical investigation. Moreover, the minimum duration of oliguria (6 hours) is based on clinical experience and was never experimentally determined. We used a massive database of ICU patients (MIMIC) to continuously vary the observation period and threshold of urine output measurements to determine optimal AKI definitions for improved in-hospital mortality prediction.


After excluding end-stage renal disease, 14,536 adult patients were included. Various AKI thresholds corresponding to different observation periods and urine output measurement thresholds were analyzed using a multivariate logistic regression model for each choice of thresholds. A total of 470 regression models were plotted. We controlled for sex, age, SOFA and co-morbidities (ICD-9 codes). To visualize dependence of adjusted mortality rate and mortality predictive power on AKI definition, we generated 3 D and contour plots.


The UO versus mortality plot demonstrates that when UO <0.5 the mortality rate increases rapidly as urine output decreases. Mortality increases sharply for observation periods up to 5 hours and then the rate of increase is reduced until a plateau is reached at approximately 24 hours. Cross-sections at 6, 12 and 24 hours of the UO mortality plot shows that the mortality rate of AKI 1 and AKI 2 are similar but differ significantly from AKI 3. See Figure 1.

Figure 1

(a), (b) Urine output mortality plot. (c) Cross-section at 6, 12, 24 hours.


The current AKIN recommendation that uses a urine output of 0.5 ml/kg/hour is valid. Since AKIN's stages 1 and 2 were found to exhibit similar mortality rates, we propose a reduction in the AKI 2 threshold to 0.4 ml/kg/hour to better delineate among the three stages. We demonstrated that the mortality rate increases sharply during the first 5 hours of oliguria. Hence, the current used observation period (6 hours) seems to be valid.

Author information



Corresponding author

Correspondence to T Mandelbaum.

Rights and permissions

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, 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 changes were made. 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 The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and Permissions

About this article

Cite this article

Mandelbaum, T., Scott, D., Lee, J. et al. Validation of the AKIN criteria definition using high-resolution ICU data from the MIMIC-II database. Crit Care 15, P105 (2011).

Download citation


  • Acute Kidney Injury
  • Urine Output
  • Multivariate Logistic Regression Model
  • Hourly Urine
  • Criterion Definition