Does increased glomerular filtration rate or disturbed tubular function early in the course of childhood type 1 diabetes predict the development of nephropathy?

To clarify whether glomerular hyperfiltration or disturbances in renal tubular function may be early markers of the later development of nephropathy a follow-up study was performed in 34 young Type 1 diabetic patients, who had originally been investigated 12 years previously. The initial median age was 14 (range 7-18) years and median diabetes duration 7 (2-14) years. At initial examination only one of the 34 diabetic patients exhibited increased urinary albumin excretion rate. The median glomerular filtration rate was increased (136 vs 107 ml min-1 1.73 m-2; p less than 0.0001) and median threshold concentration of phosphate per litre of glomerular filtrate was decreased (1.27 vs 1.76 mmol l-1; p less than 0.0001) in the diabetic group as compared to that of 28 healthy children. At follow-up 17 patients showed increased urinary albumin excretion rate and the median glomerular filtration rate in this group was significantly lower than that of 17 patients with normal urinary albumin excretion rate (108 vs 125 ml min-1 1.73 m-2; p less than 0.05). However, no relationships were found between the increased urinary albumin excretion (incipient and/or overt diabetic nephropathy) at follow-up to either the initial glomerular filtration rate (134 vs 137 ml min-1 1.73 m-2; p greater than 0.05) or to renal tubular function assessed from urinary excretion rate of beta 2-microglobulin (0.059 vs 0.069 microgram min-1; p greater than 0.05) and the renal threshold concentration of phosphate per litre of glomerular filtrate (1.29 vs 1.22 mmol l-1; p greater than 0.05).