Perioperative change in creatinine following cardiac surgery with cardiopulmonary bypass is useful in predicting acute kidney injury: a single-centre retrospective cohort study

OBJECTIVES: 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