Nickolas TL et al. (2008) Sensitivity and specificity of a single emergency department measurement of urinary neutrophil gelatinase-associated lipocalin for diagnosing acute kidney injury. Ann Intern Med 148: 810–819

Serum creatinine levels rise several days after acute kidney injury but are an insensitive marker of kidney function. Urinary levels of neutrophil gelatinase-associated lipocalin (NGAL) correlate with the severity of ongoing renal tubular damage and represent one possible alternative marker. Studies of NGAL conducted to date in the setting of acute kidney injury have generally involved patients with injury of a specific cause and known timing.

Nickolas and colleagues' prospective study included 635 patients (mean age 60 years) admitted to a hospital emergency room. Final diagnoses included 30 patients with acute kidney injury, 88 with prerenal azotemia, and 106 with nonprogressive chronic kidney disease; the other 411 patients had normal kidney function. NGAL and other biomarkers (creatinine, α1-microglobulin, α1-acid glycoprotein and N-acetyl-β-D-glucosaminidase) were assessed in patients' samples of blood and urine obtained at admission.

In this heterogeneous cohort of patients, NGAL was the most useful biomarker. Only patients diagnosed on the basis of clinical criteria as having acute kidney injury had significantly elevated urinary levels of NGAL at admission, regardless of the mechanism of injury. Maximal sensitivity and specificity of NGAL was achieved with a cutoff of 130 µg/g creatinine; levels above this threshold predicted excess morbidity and poor outcomes. NGAL levels were a better predictor of outcome than the other markers of acute kidney injury tested and remained highly diagnostic even when the time of injury was unknown.