BACKGROUND: Neutrophil gelatinase-associated lipocalin (NGAL) has recently been introduced as a renal biomarker and an increase in its level suggests tubular injury. Diabetic nephropathy, a leading cause of end-stage renal disease, causes typical changes characterized by glomerulosclerosis and eventual tubular damage in the kidney. In the present study, we attempted to validate the usefulness of plasma NGAL (pNGAL) as a biomarker for tubular damage in diabetic nephropathy. METHODS: The plasma NGAL levels of 260 diabetes mellitus patients and 50 healthy individuals werewas measured by means of fluorescent immunoassay using with the Triage NGAL test (Biosite, USA). The patients were divided into 3 groups on the basis of their urinary albumin excretion (UAE) levels, and the pNGAL differences among each group were analyzed. The degree of albuminuria and cystatin C-based glomerular filtration rate (GFR) were also compared with the pNGAL levels. RESULTS: The mean pNGAL levels of the normal subjects and diabetic patients were 61.9 +/- 4.81 ng/mL and 93.4 +/- 71.78 ng/mL, respectively. pNGAL level was significantly increased in patients with severe albuminuria (P < 0.001). The pNGAL level was found to be positively correlated with the degree of albuminuria (R2 = 0.218, P < 0.001) and inversely correlated with GFR (R2 = 0.269, P < 0.001). Particularly, the pNGAL level of patients with diabetic nephropathy was found to be associated with the renal damage and independent of other factors influencing the renal damage (R2 = 0.218). CONCLUSIONS: pNGAL level independently reflects renal damage in patients with diabetic nephropathy. Measurement of pNGAL level combined with UAE would help enable to detect both glomerular and tubular damage in diabetic nephropathy patients.