Quantitative assessment of urinary protein and enzyme excretion--a diagnostic programme for the detection of renal involvement in type I diabetes mellitus.

In an effort to establish a reliable programme for the clinical monitoring of renal involvement in patients with type-I diabetes mellitus, we quantified the urinary excretion of immunoglobulin G (IgG), transferrin (Tf), albumin (Alb), alpha 1-microglobulin (alpha 1MG), N-acetyl-beta-D-glucosaminidase (NAG), and total protein in 130 dipstick negative children and young adults with type-I diabetes. Eighty-five sex- and age-matched healthy persons served as a control group for the definition of the upper reference limits (95th centiles; micrograms min-1 1.73 m2): transferrin 1.4; albumin 16.6; total protein 27.1; NAG: 2.0 mU min-1 1.73 m2. Sex-related differences were detected for IgG (men: 3.8; women: 1.7) and alpha 1 MG (men: 6.0; women: 4.0 micrograms min-1 1.73 m2). The urinary excretion of IgG, Tf, alpha 1MG, NAG, and total protein was significantly higher in subjects with diabetes when compared to healthy controls (p < 0.01). Furthermore, 20 patients (15%) showed an elevated excretion of tubular markers (alpha 1MG and NAG), and 3 patients (2%) of at least two glomerular markers (Alb and/or Tf and/or IgG). Additionally, 18 individuals (14%) presented a mixed excretion pattern of both tubular and glomerular markers. These data suggest that the quantitation of both glomerular and tubular proteinuria provides a sensitive and cost-effective instrument for the non-invasive screening for renal involvement in patients with diabetes mellitus.