Measurement of glomerular filtration rate in children with insulin-dependent diabetes mellitus.

51Cr-EDTA, inulin and creatinine clearances were measured simultaneously in 11 diabetic children and 12 healthy young adults. The clearances in all individuals were 115 +/- 24 ml/min per 1.73 m2SA for 51Cr-EDTA, 118 +/- 25 ml/min per 1.73 m2SA for inulin and 157 +/- 35 ml/min per 1.73 m2SA for creatinine. Values were higher in the diabetic children but the differences were not significant. 51Cr-EDTA clearance significantly underestimated that of inulin by a mean of -7.4 +/- 2.5 (SEM) ml/min per 1.73 m2SA (p less than 0.01) and creatinine clearance significantly overestimated that of inulin by 37.6 +/- 3.3 (SEM) ml/min per 1.73 m2SA (p less than 0.0001). Similarly, the mean ratio of 51Cr-EDTA to inulin clearance was 0.94 (95% CI 0.90-0.98) and that of creatinine to inulin clearance was 1.32 (95% CI 1.27-1.37); the differences between diabetics and controls were not significant. Correlation coefficients were 0.93 between 51Cr-EDTA and inulin clearances, and 0.95 between inulin and creatinine clearances. The pooled coefficient of variation between clearances within an individual was higher with inulin, 10.3 +/- 6.5% (SD), than 51Cr-EDTA, 7.3 +/- 5.1% (p less than 0.001, t test). These results show that 51Cr-EDTA clearance underestimates that of inulin to a similar extent in both diabetic children and healthy controls and creatinine clearance overestimates inulin clearance to a greater but similar extent in both groups. The methodological variation in 51Cr-EDTA measurement is less than with the other 2 methods. Therefore, we recommend the use of the renal clearance of 51Cr-EDTA for the measurement of GFR in diabetic children.

Renal tubular proteinuria and microalbuminuria in diabetic patients.

The urinary extraction of albumin, retinol binding protein, and N-acetyl-beta-D-glucosaminidase were studied in 60 children with insulin dependent diabetes mellitus and in 45 normal children to find out whether the renal tubules played a part in causing the early increase in urinary excretion of albumin that occurs in diabetes mellitus. Two overnight urine samples were collected and the protein excretion measured and expressed as the geometric mean of the protein to creatinine ratio (urinary albumin:creatinine ratio, urinary retinol binding protein:creatinine ratio, and urinary N-acetyl-beta-D-glucosaminidase:creatinine ratio, respectively). The excretion of all three proteins was significantly higher in the diabetic children with 15 (25%) of urinary albumin:creatinine ratio, 16 (27%) of urinary retinol binding protein:creatinine ratio, and 43 (72%) of urinary N-acetyl-beta-D-glucosaminidase:creatinine ratio values being above the normal range. Significant correlations were observed between urinary albumin:creatinine ratio and urinary retinol binding protein:creatinine ratio, urinary albumin:creatinine ratio and urinary N-acetyl-beta-D-glucosaminidase:creatinine ratio, and urinary retinol binding protein:creatinine ratio and urinary N-acetyl-beta-D-glucosaminidase:creatinine ratio. There were also significant correlations between glycated haemoglobin 1c (HbA1c) and these proteins, especially N-acetyl-beta-D-glucosaminidase. No correlations were observed with the fractional excretion of sodium, flow rate of urine, glomerular filtration rate, or blood pressure. These data show that tubular abnormalities are present early in the course of insulin dependent diabetes mellitus and suggest that the early increase in urinary excretion of albumin may be at least partly tubular in origin, and that glycaemic control may influence this aspect of proximal tubular function.