title: Validity of the International Classification of Diseases, Tenth Revision code for acute kidney injury in elderly patients at presentation to the emergency department and at hospital admission.
abstract: OBJECTIVE
  To evaluate the validity of the International Classification of Diseases, Tenth Revision (ICD-10) code N17x for acute kidney injury (AKI) in elderly patients in two settings: at presentation to the emergency department and at hospital admission.
  
  
  METHODS
  A population-based retrospective validation study.
  
  
  METHODS
  Southwestern Ontario, Canada, from 2003 to 2010.
  
  
  METHODS
  Elderly patients with serum creatinine measurements at presentation to the emergency department (n=36 049) or hospital admission (n=38 566). The baseline serum creatinine measurement was a median of 102 and 39 days prior to presentation to the emergency department and hospital admission, respectively.
  
  
  METHODS
  Sensitivity, specificity and positive and negative predictive values of ICD-10 diagnostic coding algorithms for AKI using a reference standard based on changes in serum creatinine from the baseline value. Median changes in serum creatinine of patients who were code positive and code negative for AKI.
  
  
  RESULTS
  The sensitivity of the best-performing coding algorithm for AKI (defined as a ≥2-fold increase in serum creatinine concentration) was 37.4% (95% CI 32.1% to 43.1%) at presentation to the emergency department and 61.6% (95% CI 57.5% to 65.5%) at hospital admission. The specificity was greater than 95% in both settings. In patients who were code positive for AKI, the median (IQR) increase in serum creatinine from the baseline was 133 (62 to 288) µmol/l at presentation to the emergency department and 98 (43 to 200) µmol/l at hospital admission. In those who were code negative, the increase in serum creatinine was 2 (-8 to 14) and 6 (-4 to 20) µmol/l, respectively.
  
  
  CONCLUSIONS
  The presence or absence of ICD-10 code N17× differentiates two groups of patients with distinct changes in serum creatinine at the time of a hospital encounter. However, the code underestimates the true incidence of AKI due to a limited sensitivity.
authors.affiliation: Division of Nephrology, Department of Medicine,  Western University, London, Ontario,  Canada.
authors.forename: Y Joseph
authors.initials: YJ
authors.lastname: Hwang
authors.forename: Salimah Z
authors.initials: SZ
authors.lastname: Shariff
authors.forename: Sonja
authors.initials: S
authors.lastname: Gandhi
authors.forename: Ron
authors.initials: R
authors.lastname: Wald
authors.forename: Edward
authors.initials: E
authors.lastname: Clark
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Fleet
authors.forename: Amit X
authors.initials: AX
authors.lastname: Garg