LOW-MOLECULAR-MASS PROTEINURIA AS A MARKER OF PROXIMAL RENAL TUBULAR DYSFUNCTION IN NORMOALBUMINURIC AND MICROALBUMINURIC NON-INSULIN-DEPENDENT DIABETIC SUBJECTS

We determined the urinary excretion, expressed as the protein/creatinine ratio (morning urines), of albumin (a marker of glomerular dysfunction) and retinol-binding protein (RBP; a low-molecular-mass protein marker of tubular proteinuria) in 102 non-insulin-dependent diabetic patients. There was a statistically significant (P <0.00001) correlation (rho = 0.38) between the urinary excretion values of the two proteins. The population could be divided into four subgroups: 32 with normal excretion values, 15 with above-normal urinary excretion of RBP, 24 with above-normal urinary excretion of albumin, and 31 patients with above-normal urinary excretion of both proteins. No patients had above-normal serum creatinine concentrations or above-normal serum RBP concentrations. This seems to exclude ''tubular overflow proteinuria'' as the cause of the increased urinary excretion of RBP seen in some patients with non-insulin-dependent diabetes. Our data suggest the presence of a state of proximal tubular dysfunction in these patients.