Comparison of urinary neutrophil glucosaminidase-associated lipocalin, cystatin C, and α1-microglobulin for early detection of acute renal injury after cardiac surgery

Objective: Acute renal injury is a frequent complication after cardiac surgery that necessitates additional treatment and increases mortality. To apply measures for optimizing renal function in a well-directed and effective way, it is most important to detect acute kidney injury at an early stage. The present study compares three markers of renal tubular function for detection of acute renal injury according to the acute kidney injury (Acute Kidney Injury Network (AKIN)) criteria. Methods: Urinary concentration of the tubular markers neutrophil glucosaminidase-associated lipocalin (NGAL), alpha(1)-microglobulin (alpha(1)MG), and cystatin C (CysC) were measured in 50 patients after elective cardiac surgery. Samples were taken once preoperatively and postoperatively every 12 h for up to 5 days. Based on the highest recorded postoperative AKIN score, patients were divided into two groups (AKIN 0 and AKIN 1-3). Statistical analysis was done for marker concentrations at three time points: preoperative, after admission to the intensive care unit (ICU), and at the highest postoperative AKIN level. In addition, all concentrations of marker proteins were multiplied by the ratio of creatinine concentrations in serum and urine; these products were also analyzed statistically. In this way, we were able to eliminate the influence of varying degrees of diuresis on marker concentrations. Results: As early as at admission to the ICU, all marker proteins showed significantly higher concentrations compared with preoperative values. However, differences in concentrations between the groups AKIN 0 and AKIN 1-3 were only statistically significant for NGAL. Using receiver operating characteristic (ROC) analysis, we found that only NGAL concentrations were suitable for detecting acute kidney injury with adequate sensitivity and specificity (area under the curve (AUC) = 0.773). Levels of alpha(1)MG yielded a comparable accuracy when urinary concentrations were multiplied by the serum/urine creatinine ratio (AUC = 0.712). Conclusion: An increase in urinary NGAL is an early sign of acute kidney injury after cardiac surgery. After multiplication by the serum/urine creatinine ratio, urinary alpha(1)MG is also suitable for detection of acute kidney injury at an early stage. (C) 2010 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.