Tubular dysfunction in the early stage of diabetic nephropathy.

Renal tubular function was investigated in 98 non-insulin-dependent and 18 insulin-dependent diabetics under conditions of standard glycemic control. Mean urinary excretion of lysozyme, beta 2-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG) in both Albustix-negative and positive patients were significantly elevated above the control range. The increased excretion of lysozyme, beta 2-microglobulin and NAG was found in 21, 55 and 62% of the normoalbuminuric patients, and in 40, 57 and 74% of the microalbuminuric patients, respectively. Besides the parameters cited above, urinary acid-soluble glycoprotein (ASP) was measured to assess its potential as an indicator of early renal dysfunction. Mean urinary ASP excretion was also elevated in both Albustix-negative and positive patients. The albumin/ASP ratio increased as nephropathy advanced. Such a mode of excretion was similar to those of low-molecular-weight proteins (lysozyme and beta 2-microglobulin). The results of multiple regression analysis showed that serum creatinine most highly correlated with the excretion of the urinary proteins except for NAG.