Sensitivity and specificity of a single emergency department measurement of urinary neutrophil gelatinase-associated lipocalin for diagnosing acute kidney injury

Background: A single serum creatinine measurement cannot distinguish acute kidney injury from chronic kidney disease or prerenal azotemia. Objective: To test the sensitivity and specificity of a single measurement of urinary neutrophil gelatinase-associated lipocalin (NGAL) and other urinary proteins to detect acute kidney injury in a spectrum of patients. Design: Prospective cohort study. Setting: Emergency department of Columbia University Medical Center, New York, New York. Participants: 635 patients admitted to the hospital with acute kidney injury, prerenal azotemia, chronic kidney disease, or normal kidney function. Measurements: Diagnosis of acute kidney injury was based on the RIFLE (risk, injury, failure, loss, and end-stage) criteria and assigned by researchers who were blinded to experimental measurements. Urinary NGAL was measured by immunoblot, N-acetyl-beta-D-glucosaminidase (NAG) by enzyme measurement, alpha(1)-microglobulin and alpha(1)-acid glycoprotein by immunonephelometry, and serum creatinine by Jaffe kinetic reaction. Experimental measurements were not available to treating physicians. Results: Patients with acute kidney injury had a significantly elevated mean urinary NGAL level compared with the other kidney function groups (416 mu g/g creatinine [SD, 387]; P = 0.001). At a cutoff value of 130 mu g/g creatinine, sensitivity and specificity of NGAL for detecting acute injury were 0.900 (95% CI, 0.73 to 0.98) and 0.995 (CI, 0.990 to 1.00), respectively, and positive and negative likelihood ratios were 181.5 (CI, 58.33 to 564.71) and 0.10 (CI, 0.03 to 0.29); these values were superior to those for NAG, alpha(1)-microglobulin, alpha(1)-acid glycoprotein, fractional excretion of sodium, and serum creatinine. In multiple logistic regression, urinary NGAL level was highly predictive of clinical outcomes, including nephrology consultation, dialysis, and admission to the intensive care unit (odds ratio, 24.71 [CI, 7.69 to 79.42]). Limitations: All patients came from a single center. Few kidney biopsies were performed. Conclusion: A single measurement of urinary NGAL helps to distinguish acute injury from normal function, prerenal azotemia, and chronic kidney disease and predicts poor inpatient outcomes.