Variations in renal threshold for glucose in Type 1 (insulin-dependent) diabetes mellitus

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Abstract
The blood glucose/urinary glucose relationship was studied in 23 patients with Type 1 (insulin-dependent) diabetes. Glucose was infused intravenously in order to increase blood glucose concentration slowly and gradually. The renal threshold was recorded at the slightest trace of glycosuria and varied by a factor of 2 (from 6.0 to 14.3 mmol/l). The rise in blood glucose required to change the urinary output (0–1.1 mmol glucose/20 min) varied by a factor of 7 (1.1–7.6 mmol/l). The maximal rate of tubular glucose reabsorption varied by a factor of 2 (0.93–1.98 mmol/min). The renal threshold was negatively correlated with the creatinine clearance (r=-0.52, pr=-0.47, pr=-0.54, p< 0.05). In conclusion, urinary glucose excretion is dependent on both renal threshold and the splay and the slope of the blood glucose/urinary glucose excretion curve. Thus, the degree of glycosuria is of value as an index of diabetic control only when the blood glucose/urinary glucose relationship is known. The inverse correlation between renal threshold and creatinine clearance limits the usefulness of measuring glycosuria in patients with nephropathy.