title: Prognostic implications of adding urine output to serum creatinine measurements for staging of acute kidney injury after major surgery: a cohort study.
abstract: Current guidelines recommend staging acute kidney injury (AKI) according to the serum creatinine (SCr) or urine output (UO) criteria that achieve the highest stage. There is little information about the implications of adding UO to SCr measurements for staging AKI outside intensive care units and after cardiac surgery.
  
  
  
  We performed a cohort study of all adults without end-stage renal disease who underwent major noncardiac surgery between January 2005 and March 2011 in Calgary, AB, Canada. Participants required at least two SCr and UO measurements to be included. We examined the implications of adding UO to SCr to stage AKI based on Kidney Disease: Improving Global Outcomes criteria. Logistic and linear regression models were used to examine the associations between AKI stage and 30-day mortality or hospital length of stay (LOS), respectively.
  
  
  
  A total of 4229 (17%) surgical patients had sufficient SCr and UO measurements for inclusion in the cohort. The apparent incidence of postoperative AKI substantially increased with the addition of UO to SCr criteria (8.1% with SCr alone versus 64.0% with SCr and UO). Mortality for a given stage of AKI was lower when UO was added to SCr criteria (0.3, 3.2, 1.9 and 3.0% for no AKI and Stages 1, 2 and 3, respectively) versus with SCr alone (1.2, 4.2, 15.4 and 12.8%). However, among participants without AKI based on the SCr criterion, the odds of mortality and mean LOS both significantly increased with lower UO. Models that reclassified AKI stage based on UO in addition SCr criteria had the best discrimination for mortality and LOS.
  
  
  
  Adding UO to SCr criteria substantially increases the apparent incidence of AKI on hospital wards and significantly changes the prognostic implications of AKI identification and staging. These measures should not be considered equivalent criteria in AKI staging.
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Samuel
authors.initials: S
authors.lastname: Quan
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, AB, Canada.
authors.forename: Neesh
authors.initials: N
authors.lastname: Pannu
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Todd
authors.initials: T
authors.lastname: Wilson
authors.affiliation: Department of Surgery, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Chad
authors.initials: C
authors.lastname: Ball
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Tan
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.|Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Marcello
authors.initials: M
authors.lastname: Tonelli
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.|Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Hemmelgarn
authors.affiliation: Department of Surgery, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.|Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Elijah
authors.initials: E
authors.lastname: Dixon
authors.affiliation: Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.|Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: James
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood / Q000209:etiology / Q000473:pathology* / Q000652:urine; D000368:Aged; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007362:Intensive Care Units; D007677:Kidney Function Tests; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D017582:Renal Replacement Therapy / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D014554:Urination
chemical_list: D003404:Creatinine
keywords: acute kidney injury; prognosis; risk stratification; surgery; urine output