To the Editor: 

We read with great interest the review of Cardiopulmonary Bypass-associated Acute Kidney Injury by Kumar and Suneja,1published in the April 2011 issue, and we thank the authors for their excellent work. However, with regard to early detection of acute kidney injury (AKI) in adults by means of neutrophil gelatinase-associated lipocalin (NGAL), we feel that there has been a positive selection bias in their review of the available evidence.

Although they imply that, in adult patients after cardiopulmonary bypass cardiac surgery, plasma and urine NGAL concentrations are good predictors of renal injury with area under the receiver-operating characteristic curve (AUCROC) of 0.80 and 0.96, respectively, that is in fact an exceptional result from a single, small study.2Wagener et al.  reported an AUCROCfor early diagnosis of AKI by urinary NGAL of 0.61 at 18 h postcardiopulmonary bypass. The sensitivity and specificity of urinary NGAL in predicting AKI, as judged by AUCROC, was poor, varying from 0.57 to 0.61.3Koyner et al.  4reported an AUCROCof 0.54 at 6 h postcardiopulmonary bypass for the diagnosis of AKI by plasma NGAL. Perry et al.  5documented increased plasma NGAL levels in patients who suffered AKI but the sensitivity was as low as 38.7%. Haase et al.  6in a recent meta-analysis derived an AUCROCof 0.78 for early diagnosis of AKI after cardiac surgery by plasma and urinary NGAL.

Given the limited sensitivity and specificity of individual biomarkers, it may be more realistic to use a panel of biomarkers to predict AKI and outcome. Furthermore, a number of key issues, including the wide variability in reported diagnostic performance, require clarification before adoption of NGAL into clinical practice.

Kumar AB, Suneja M: Cardiopulmonary bypass-associated acute kidney injury. ANESTHESIOLOGY 2011; 114:964–70
Tuladhar SM, Püntmann VO, Soni M, Punjabi PP, Bogle RG: Rapid detection of acute kidney injury by plasma and urinary neutrophil gelatinase-associated lipocalin after cardiopulmonary bypass. J Cardiovasc Pharmacol 2009; 53:261–6
Wagener G, Gubitosa G, Wang S, Borregaard N, Kim M, Lee HT: Urinary neutrophil gelatinase-associated lipocalin and acute kidney injury after cardiac surgery. Am J Kidney Dis 2008; 52:425–33
Koyner JL, Bennett MR, Worcester EM, Ma Q, Raman J, Jeevanandam V, Kasza KE, O'Connor MF, Konczal DJ, Trevino S, Devarajan P, Murray PT: Urinary cystatin C as an early biomarker of acute kidney injury following adult cardiothoracic surgery. Kidney Int 2008; 74:1059–69
Perry TE, Muehlschlegel JD, Liu KY, Fox AA, Collard CD, Shernan SK, Body SC, CABG Genomics Investigators: Plasma neutrophil gelatinase-associated lipocalin and acute postoperative kidney injury in adult cardiac surgical patients. Anesth Analg 2010;110:1541–7
Haase M, Bellomo R, Devarajan P, Schlattmann P, Haase-Fielitz A, NGAL Meta-analysis Investigator Group: Accuracy of neutrophil gelatinase-associated lipocalin (NGAL) in diagnosis and prognosis in acute kidney injury: A systematic review and meta-analysis. Am J Kidney Dis 2009;54:1012–24