Measurement of Combined Serum-Urine Cystatin C, Neutrophil Gelatinase-Associated Lipocalin, and Retinol-Binding Protein in Early Diabetic Nephropathy.

This study aimed to validate latex immunoturbidimetric assays for cystatin C (Cys-C), neutrophil gelatinase-associated lipocalin (NGAL), and retinol-binding protein (RBP), and to evaluate their combined clinical value for the early diagnosis of diabetic nephropathy (DN). In addition, a comparison was made between the diagnostic efficacy of serum and urine samples. The study comprised 100 patients with early DN and 100 control subjects. Serum and urine levels of Cys-C, NGAL, and RBP were measured using an analyzer. Method verification demonstrated that all assays were performed in accordance with the manufacturer's specifications, with high accuracy, precision, and correlation with reference methods. Serum Cys-C, NGAL, RBP-S, and their urinary counterparts were significantly higher in the DN group (p < 0.05). The combined detection of serum Cys-C, NGAL, and RBP-S provided a diagnostic sensitivity of 89.0%, specificity of 92.0%, and an AUC of 0.935. The corresponding urinary panel achieved a sensitivity of 82.0%, specificity of 88.0%, and an AUC of 0.876. In conclusion, the assays are reliable. The combined detection of Cys-C, NGAL, and RBP in serum offers the highest diagnostic value for early DN, while urine analysis provides complementary information about tubular injury.