title: Perioperative change in creatinine following cardiac surgery with cardiopulmonary bypass is useful in predicting acute kidney injury: a single-centre retrospective cohort study.
abstract: OBJECTIVE
  Acute kidney injury is common following cardiac surgery. Experimental models of acute kidney injury suggest that successful therapy should be implemented within 24-48 h of renal injury. However, it is difficult to detect acute kidney injury shortly after cardiac surgery, because creatinine concentration is diluted by cardiopulmonary bypass. We hypothesized that, following cardiopulmonary bypass, creatinine reduction ratios would correlate with haematocrit reduction ratios and would be associated with the incidence of acute kidney injury.
  
  
  METHODS
  We collected demographic and blood test data from consecutive patients (n = 1137) who had undergone cardiac surgery with cardiopulmonary bypass. The creatinine reduction ratio was calculated as follows: (preoperative creatinine-postoperative creatinine)/preoperative creatinine. Patients were assigned to either of two groups. The first group (Group 1) was used to determine the threshold for acute kidney injury, and the second group (Group 2) was used to assess diagnostic performance. Acute kidney injury was defined as an increase in serum creatinine level >0.3 mg/dl or >150% from baseline.
  
  
  RESULTS
  The incidence of acute kidney injury was 14.5% (79/545) in Group 1 and 15.5% (92/592) in Group 2. Postoperatively, creatinine concentration correlated strongly with haematocrit concentration (Pearson's r(2): 0.91). In Group 1, the area under the receiver operating characteristic curve, sensitivity and specificity were 0.71, 64.1 and 66.4%, respectively, for creatinine reduction ratios of <20%. In Group 2, the odds ratio, positive predictive value, negative predictive value and relative risk for creatinine reduction ratio performance were 4.3 (95% confidence interval 2.6-7.0), 0.27 (0.21-0.32), 0.92 (0.89-0.95) and 3.42 (2.22-5.27), respectively.
  
  
  CONCLUSIONS
  The creatinine reduction ratio may be associated with perioperative renal injury. Therefore, it is a good diagnostic indicator with high performance, and may be useful in detecting acute kidney injury at an earlier stage relative to conventional means. In addition, using creatinine reduction ratios in this manner is financially feasible.
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Yokohama, Japan shunty5323@gmail.com.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Takaki
authors.affiliation: Department of Intensive Care, Prince of Wales Hospital, Sydney, Australia.
authors.forename: Yahya
authors.initials: Y
authors.lastname: Shehabi
authors.affiliation: Christchurch and Emergency Department, University of Otago, Christchurch Hospital, Christchurch, New Zealand.
authors.forename: John W
authors.initials: JW
authors.lastname: Pickering
authors.affiliation: Department of Nephrology, Prince of Wales Hospital, Sydney, Australia.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Endre
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Yokohama, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Miyashita
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Yokohama, Japan.
authors.forename: Takahisa
authors.initials: T
authors.lastname: Goto
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood* / Q000209:etiology; D000368:Aged; D000369:Aged, 80 and over; D006348:Cardiac Surgical Procedures / Q000009:adverse effects; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D003404:Creatinine / Q000097:blood*; D006801:Humans; D008875:Middle Aged; D059035:Perioperative Period; D011237:Predictive Value of Tests; D012189:Retrospective Studies
chemical_list: D003404:Creatinine
keywords: Acute kidney injury; Cardiopulmonary bypass; Dilution of creatinine