Introduction: Neutrophil gelatinase-associated lipocalin (NGAL) is emerging as a promising new biomarker for the early identification of acute kidney injury (AKI). We have determined a reference range in a large healthy population. In addition, as NGAL is a neutrophil-related protein, we investigated whether the presence of leukocyturia has the potential to significantly alter the specificity of NGAL in the diagnosis of AKI. Methods: One hundred and seventy-four subjects (100 men, 74 women ranging from 19 to 88 y) were included in the reference population. Urinary NGAL was analysed on the Abbott ARCHITECT and results expressed in mass (mg/L) and also normalized to urinary creatinine (mg/mmol). Fifty-two leukocyturic urine samples were also analysed for NGAL. Results: The 95th centile for NGAL was determined to be 107 mg/L (13 mg/mmol). There were significant gender-related differences for NGAL, with women having higher concentrations. There were significant age-related differences for NGAL between the 40-59 and 60-88 y age categories. There were significant age-related differences between the ,40 and 60-88 y categories when NGAL was normalized to creatinine. In addition, we found significantly higher concentrations of NGAL in leukocyturia (P , 0.0001). Conclusions: We have established a 95th centile cut-off for urinary NGAL in a reference population. We have demonstrated the important potential interference of leukocyturia in confounding the interpretation of NGAL in the diagnosis of AKI.

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