title: Are surrogate assumptions and use of diuretics associated with diagnosis and staging of acute kidney injury after cardiac surgery?
abstract: OBJECTIVE
  This study measured the association between the Acute Kidney Injury Network (AKIN) diagnostic and staging criteria and surrogates for baseline serum creatinine (SCr) and body weight, compared urine output (UO) with SCr criteria, and assessed the relationships between use of diuretics and calibration between criteria and prediction of outcomes.
  
  
  METHODS
  This was a retrospective cohort study using prospective measurements of SCr, hourly UO, body weight, and drug administration records from 5701 patients admitted, after cardiac surgery, to a cardiac intensive care unit between 1995 and 2006.
  
  
  RESULTS
  More patients (n=2424, 42.5%) met SCr diagnostic criteria with calculated SCr assuming a baseline estimated GFR of 75 ml/min per 1.73 m(2) than with known baseline SCr (n=1043, 18.3%). Fewer patients (n=484, 8.5%) met UO diagnostic criteria with assumed body weight (70 kg) than with known weight (n=624, 10.9%). Agreement between SCr and UO criteria was fair (κ=0.28; 95% confidence interval 0.25-0.31). UO diagnostic criteria were specific (0.95; 0.94-0.95) but insensitive (0.36; 0.33-0.39) compared with SCr. Intravenous diuretics were associated with higher probability of falling below the UO diagnostic threshold compared with SCr, higher 30-day mortality (relative risk, 2.27; 1.08-4.76), and the need for renal support (4.35; 1.82-10.4) compared with no diuretics.
  
  
  CONCLUSIONS
  Common surrogates for baseline estimated GFR and body weight were associated with misclassification of AKIN stage. UO criteria were insensitive compared with SCr. Intravenous diuretic use further reduced agreement and confounded association between AKIN stage and 30-day mortality or need for renal support.
authors.affiliation: Regional Medical Physics, Newcastle upon TyneHospitals NHS Trust, Newcastle upon Tyne, United Kingdom. andrew.sims@nuth.nhs.uk
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Sims
authors.forename: Hayder K
authors.initials: HK
authors.lastname: Hussein
authors.forename: Mahesh
authors.initials: M
authors.lastname: Prabhu
authors.forename: N Suren
authors.initials: NS
authors.lastname: Kanagasundaram
mesh_terms: D058186:Acute Kidney Injury / Q000145:classification / Q000175:diagnosis* / Q000401:mortality; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001835:Body Weight; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood; D004232:Diuretics; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D017582:Renal Replacement Therapy; D012189:Retrospective Studies
chemical_list: D004232:Diuretics; D003404:Creatinine