title: The calculation of baseline serum creatinine overestimates the diagnosis of acute kidney injury in patients undergoing cardiac surgery.
abstract: OBJECTIVE
  The current definition and classification of acute kidney injury is based on consensus criteria (RIFLE and AKIN systems). Creatinine is the most commonly used of the recommended parameters (creatinine, glomerular filtration rate and diuresis). If the baseline value is not known, it can be calculated based on the simplified MDRD equation, assuming a filtration rate of 75 ml/min/1.73 m2 for the calculation. The aim of this study was to evaluate the diagnostic impact of using estimated baseline creatinine compared to the actual value measured in patients undergoing cardiac surgery.
  
  
  METHODS
  Analysis of patients undergoing major cardiac surgery, who were prospectively included in a database. The maximum RIFLE stage reached was calculated for each patient using the measured and estimated baseline creatinine levels. The impact on the diagnosis was analysed using intraclass correlation coefficients, concordance analysis and Bland-Altman plots.
  
  
  RESULTS
  The incidence of postoperative acute kidney injury in 2103 cases between 2002 and 2007 was 29.1%, according to estimated creatinine (14.3% with the measure). This represents an overestimation of 104%, with an intraclass correlation of 0.12. By excluding patients with known chronic kidney disease (glomerular filtration rate [<60 ml/min/1.73 m2), both the overestimation (2.4%) and the correlation (0.57) improved.
  
  
  CONCLUSIONS
  The calculation of baseline creatinine using the MDRD equation overestimates the incidence of acute kidney injury after cardiac surgery, and is an inadequate method for detection when the baseline value is unknown.
authors.affiliation: Anaesthesiology and Resuscitation Department, Ramón y Cajal University Hospital, Ramón y Cajal Institute of Health Research, IRYCIS, Acute Kidney Failure Research Consortium, CIFRA, Madrid, Spain. acandela.hrc@salud.madrid.org
authors.forename: A M
authors.initials: AM
authors.lastname: Candela-Toha
authors.forename: M
authors.initials: M
authors.lastname: Recio-Vázquez
authors.forename: A
authors.initials: A
authors.lastname: Delgado-Montero
authors.forename: J M
authors.initials: JM
authors.lastname: del Rey
authors.forename: A
authors.initials: A
authors.lastname: Muriel
authors.forename: F
authors.initials: F
authors.lastname: Liaño
authors.forename: T
authors.initials: T
authors.lastname: Tenorio
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood* / Q000175:diagnosis*; D000368:Aged; D006348:Cardiac Surgical Procedures; D003404:Creatinine / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D011183:Postoperative Complications / Q000097:blood* / Q000175:diagnosis*; D011446:Prospective Studies
chemical_list: D003404:Creatinine