Reduction in mean glomerular pore size coincides with the development of large shunt pores in patients with diabetic nephropathy

The glomerular size selectivity was determined by neutral dextran clearance sieving technique and plasma cystatin C levels in two groups of patients w ith long-standing type I diabetes mellitus and different stages of albuminu ria but normal glomerular filtration rate and in a group of healthy control s. The sieving characteristics of the glomerular filter were determined usi ng a mathematical model of log normal pore size distribution. Patients with albuminuria above 200 mu g/min exhibited a significant increase of cystati n c plasma concentrations and a significant reduction in mean glomerular fi ltration slit size. Only these patients exhibited large, unrestrictive pore s in the glomerular filter (shunt), The plasma cystatin c levels correlated significantly with 26-angstrom neutral dextran plasma levels in microalbum inuric patients and in patients with albuminuria above 200 mu g/min. We con clude that a reduction in average pore size of the glomerular filter does n ot occur earlier than the development of large shunt pores. The renal clear ance of cystatin c in patients with proteinuric diabetic nephropathy but a normal glomerular filtration rate is reduced due to its molecular size. Cop yright (C) 2000 S. Karger AG, Basel.