NDT Advance Access originally published online on April 6, 2009
Nephrology Dialysis Transplantation 2009 24(9):2739-2744; doi:10.1093/ndt/gfp159
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A comparison of observed versus estimated baseline creatinine for determination of RIFLE class in patients with acute kidney injury
1 Department of Intensive Care and Department of Medicine, Austin & Repatriation Medical Centre, Melbourne, Australia 2 Division of Critical Care Medicine, University of Alberta, Edmonton, Canada 3 Intensive Care Unit, Department of Anesthesiology, Jikei University School of Medicine, Tokyo, Japan 4 Nephrology—Intensive Care, St Bortolo Hospital, Vicenza, Italy 5 Department of Anesthesiology and Resuscitology, Okayama University Medical School, Okayama, Japan 6 Department of Nephrology, University Hospital Charité, Berlin, Germany 7 Dienst Intensieve Geneeskunde, Universitair Ziekenhuis Gasthuisberg, Leuven, Belgium 8 Intensive Care Unit, Singapore General Hospital, Singapore 9 Adult Intensive Care Unit, Academic Medical Center, Amsterdam, The Netherlands 10 Nephrology Division, University of São Paulo School of Medicine, São Paulo, Brazil 11 Division of Nephrology, Department of Medicine, The University of Alabama at Birmingham, AL, USA 12 Department of Intensive Care, Onze Lieve Vrouwe Gasthius, Amsterdam, The Netherlands 13 Department of Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
Correspondence and offprint requests to: Sean M. Bagshaw; Email: bagshaw{at}ualberta.ca
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Abstract |
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Background. The RIFLE classification scheme for acute kidney injury (AKI) is based on relative changes in serum creatinine (SCr) and on urine output. The SCr criteria, therefore, require a pre-morbid baseline value. When unknown, current recommendations are to estimate a baseline SCr by the MDRD equation. However, the MDRD approach assumes a glomerular filtration rate of 
75 mL/min/1.73 m2. This method has not been validated.
Methods. Data from the Beginning and Ending Supportive Therapy for the Kidney (BEST Kidney) study, a prospective observational study from 54 ICUs in 23 countries of critically ill patients with severe AKI, were analysed. The RIFLE class was determined by using observed (o) pre-morbid and estimated (e) baseline SCr values. Agreement was evaluated by correlation coefficients and Bland–Altman plots. Sensitivity analysis by chronic kidney disease (CKD) status was performed.
Results. Seventy-six percent of patients (n = 1327) had a pre-morbid baseline SCr, and 1314 had complete data for evaluation. Forty-six percent had CKD. The median (IQR) values were 97 µmol/L (79–150) for oSCr and 88 µmol/L (71–97) for eSCr. The oSCr and eSCr determined at ICU admission and at study enrolment showed only a modest correlation (r = 0.49, r = 0.39). At ICU admission and study enrolment, eSCr misclassified 18.8% and 11.7% of patients as having AKI compared with oSCr. Exclusion of CKD patients improved the correlation between oSCr and eSCr at ICU admission and study enrolment (r = 0.90, r = 0.84) resulting in 6.6% and 4.0% being misclassified, respectively.
Conclusions. While limited, estimating baseline SCr by the MDRD equation when pre-morbid SCr is unavailable would appear to perform reasonably well for determining the RIFLE categories only if and when pre-morbid GFR was near normal. However, in patients with suspected CKD, the use of MDRD to estimate baseline SCr overestimates the incidence of AKI and should not likely be used. Improved methods to estimate baseline SCr are needed.
Keywords: acute kidney injury; consensus definition; creatinine; RIFLE criteria; validation
Received for publication: 17. 1.09
Accepted in revised form: 16. 3.09
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