Retinopathy in type II diabetes mellitus associated with above-normal urinary excretion of RBP.

We performed a cross-sectional study on the urinary excretion profiles of albumin (a marker of glomerular dysfunction) and retinol-binding protein (a low molecular mass protein marker of renal proximal tubular dysfunction) in non-insulin dependent (Type II) diabetics, with or without retinopathy. The urinary excretion of both proteins, in particular retinol-binding protein, was significantly higher in patients with background/proliferative retinopathy compared to patients without retinopathy. The degree of retinopathy correlated to the urinary excretion of albumin (P < 0.005) and retinol-binding protein (P < 0.0001). Retinopathy occurred at a higher frequency in patients with above-normal urinary excretion of retinol-binding protein, both in the absence or presence of micro/macroalbuminuria. The frequency of retinopathy among micro/macroalbuminuric patients with a normal urinary excretion of retinol-binding protein did not differ significantly from that observed in patients with a normal urinary excretion of both proteins. We cannot explain the association between retinopathy and proximal tubular dysfunction in Type II diabetes. However, it is possible that both phenomena are related to a common pathogenetic factor.