Urinary neutrophil gelatinase-associated lipocalin and acute kidney injury after cardiac surgery

Background: Neutrophil gelatinase-associated lipocalin (NGAL) is proposed as an early marker of kidney injury. We report the association of urinary NGAL with indexes of intraoperative renal hypoperfusion (cardiopulmonary bypass time and aortic cross-damp time) and acute kidney injury (AKI) after adult cardiac surgery. Study Design: Diagnostic test accuracy. Setting & Participants: Adult cardiac surgical patients (n = 426) in a single center from 2004 to 2006. Index Test: Urinary NGAL immediately and 3, 18, and 24 hours after cardiac surgery, using an enzyme-linked immunosorbent assay. Reference Test or Outcome: Serum creatinine-based definition for AKI (increase in serum creatinine from preoperative values by > 50% or > 0.3 mg/dL within 48 hours). Results: Mean urinary NGAL level was 165 +/- 663 (SD) ng/mL preoperatively, peaked immediately after cardiac surgery at 1,490 +/- 102 ng/mL, and remained significantly higher 3, 18, and 24 hours after surgery. 85 patients (20%) developed AKI. Areas under the receiver operating characteristic curve for urinary NGAL immediately after and 3, 18, and 24 hours later as a predictor for AKI were 0.573 (95% confidence interval [CI], 0.506 to 0.640), 0.603 (95% CI, 0.533 to 0.674), 0.611 (95% CI, 0.544 to 0.679), and 0.584 (95% CI, 0.510 to 0.657), respectively. Urinary NGAL, but not serum creatinine, level correlated significantly with cardiopulmonary bypass and aortic cross-clamp times. Areas under receiver operating characteristic curves for cardiopulmonary bypass time and aortic cross-clamp time to predict AKI were 0.592 (95% CI, 0.518 to 0.666) and 0.593 (95% CI, 0.523 to 0.665), respectively. Limitations: Limited sensitivity of changes in serum creatinine levels for kidney injury. Conclusions: Urinary NGAL has limited diagnostic accuracy to predict AKI defined by change in serum creatinine after cardiac surgery.