Nonalbuminuric proteinuria as a biomarker for tubular damage in early development of nephropathy with type 2 diabetic patients

AimThe aim of this study was to evaluate the association between urinary nonalbumin protein (NAP) and urinary tubular markers in early diabetic nephropathy. MethodsUrinary NAP was measured in 118 patients with type 2 diabetes with estimated glomerular filtration rates (eGFR) 60mL/min/1.73m(2). Urine levels of tubular markers [kidney injury molecule (KIM)-1, neutrophil gelatinase-assoicated lipocalin (NGAL) and liver-type fatty acid-binding protein (L-FABP)] were measured by using an Enzyme-linked immunosorbent assay (ELISA). Patients were divided into three groups according to urinary NAP values. ResultsThe urine levels of KIM-1, NGAL and L-FABP were significantly higher in the third tertile group than in the first tertile group (all p<0.001). There was a significant positive correlation between NAP and each tubular marker (KIM-1, NGAL and L-FABP) in univariate analysis (all p<0.001). Urinary NAP was positively correlated with all urinary tubular markers after adjustment for age, duration of diabetes, systolic blood pressure, eGFR, low-density lipoprotein cholesterol, HbA(1c) and albumin-to-creatinine ratio (KIM-1 r=0.170, p<0.001; NGAL r=0.142, p<0.015 and L-FABP r=0.262, p<0.001). In normoalbuminuric patients (n=58), urinary NAP was also significantly correlated with NGAL and L-FABP in multivariate regression analyses (r=0.302, p=0.030 and r=0.430, p=0.001). ConclusionsThese findings suggest that urinary NAP reflects tubular damage in the early-stage type 2 diabetic nephropathy (eGFR60mL/min/1.73m(2)). We suggest that urinary NAP could be used as a biomarker for tubular damage in clinical practice. Copyright (c) 2014 John Wiley & Sons, Ltd.