Comparison of absolute serum creatinine changes versus Kidney Disease: Improving Global Outcomes consensus definitions for characterizing stages of acute kidney injury

Abstract

Background: The Kidney Disease: Improving Global Outcomes (KDIGO) system for classification of acute kidney injury (AKI) severity utilizes a staging schema based on relative changes in serum creatinine (sCr) concentration and urine output. This study compares the in-hospital mortality associated with KDIGO-defined AKI stages and AKI stages defined by absolute sCr increases ('Delta-Creatinine').

Methods: The study included an analysis of hospital discharge and laboratory data from an urban academic medical center over a 1-year period. Including adult in-patients undergoing two or more sCr measurements, the study classified AKI stages using the KDIGO consensus standards as well as absolute increases in sCr ('Delta-Creatinine'); Stage 0, sCr increase <0.3 mg/dL, Stage 1, sCr increase 0.3-0.69 mg/dL, Stage 2, sCr increase 0.7-1.19 mg/dL and Stage 3, sCr increase ≥1.2 mg/dL or initiation of renal replacement therapy. The Delta-Creatinine cut-points were defined to optimize discrimination of in-patient mortality between AKI stages. The associations between KDIGO and Delta-Creatinine AKI stages and in-hospital mortality were compared using the time-dependent hazard ratios (HRs) and the net reclassification improvement (NRI).

Results: Of the 19 878 hospitalizations included in the analysis, the prevalence of AKI was 23.4% as defined by the KDIGO criteria. The Delta-Creatinine system discriminated the differences between adjacent AKI stages (i.e. 1 versus 0, 2 versus 1, 3 versus 3) earlier than the KDIGO system. The NRI between Delta-Creatinine and KDIGO for the prediction of mortality was 9.7% [95% confidence interval (CI) 6.2-13.2%]. Stratification by age, sex, race and history of chronic kidney disease (CKD) resulted in similar NRI values.

Conclusion: The Delta-Creatinine system, based on the absolute increases in sCr, provides a promising alternative to the KDIGO system for characterizing the severity of AKI and its associations with in-patient mortality.

Keywords: acute kidney injury; chronic kidney disease; health services; hospital mortality.

FIGURE 1:

Kaplan–Meier graphs for hospital survival, stratified by KDIGO (left) and Delta-Creatinine (right) stages of AKI. Highest survival curves represent KDIGO and Delta-Creatinine Stage 0. Lowest survival curves represent KDIGO and Delta-Creatinine Stage 3.

FIGURE 2:

Comparison of HRs of death for successive AKI stages using KDIGO and Delta-Creatinine systems. Each panel depicts the time-dependent HRs (solid lines ± 95% confidence interval) comparing successive AKI stages with the KDIGO stages in the top panels and the Delta-Creatinine categories shown in the bottom panels. The horizontal lines at HR = 1 represents equality between AKI stages. The vertical dashed line represents the time point where the 95% CI of the difference in HRs falls below or rises above HR = 1. The dashed horizontal lines indicate time-invariant HRs obtained using Cox proportional hazard multivariable regression models, adjusted for age, race and gender.

FIGURE 3:

Net reclassification of AKI from KDIGO to the Delta-Creatinine-based staging system. The percentages of each KDIGO stage reclassified upwards (rightwards) to higher or downwards (leftwards) to the lower Delta-Creatinine stage are shown in the figure. For example, for KDIGO Stage 1 AKI, while most would be reclassified as Delta-Creatinine Stage 1, 7.5% would be reclassified to the lower Delta-Creatinine Stage 0, and 13.8% would be reclassified to the higher Delta-Creatinine Stage 2. NRI 9.5% (95% CI 6.0–13.0%). Figure adapted from the CKD Prognosis Consortium (http://www.jhsph.edu/ckdpc).