Glomerular and tubular proteinuria in type 1 (insulin-dependent) diabetic patients with and without retinopathy.

We compared the urinary excretion of albumin, transferrin, N-acetyl-beta-D-glucosaminidase and alpha-1-microglobulin in 78 Type 1 (insulin-dependent) diabetic patients: 39 with retinopathy and 39 without. The two groups were matched for age, sex and duration of diabetes. The patients with retinopathy had increased excretion (median and range) of albumin [1.7(0.3-399.1) versus 1.0(0.3-116.6) mg/mmol creatinine, P less than 0.05], transferrin [114.2 (4.1-37126.2) versus 33.4 (1.0-4176.7) micrograms/mmol creatinine, P less than 0.01] and N-acetyl-beta-D-glucosaminidase [23.8 (1.1-119.1) versus 15.0 (0.1-65.1) mumol/h/mmol creatinine, P less than 0.05] but not alpha-1-microglobulin. Transferrin excretion correlated with albumin excretion. The prevalence of increased transferrin excretion (transferrinuria) was greater than that of microalbuminuria in patients both with and without retinopathy (P less than 0.01 in both cases). Urinary transferrin seems likely to be predominantly of glomerular origin and merits prospective longitudinal evaluation as a potential index of the microangiopathic process.