Dysfunction of tubular phosphate reabsorption related to glomerular filtration and blood glucose control in diabetic children.

The renal handling of inorganic phosphate was studied by measuring the urinary excretion rate of phosphate (UPO4V), phosphate-(Cr51) EDTA clearance ratio (CPO4/GFR) and maximal tubular reabsorption of phosphate per litre glomerular filtrate (TmPO4/GFR) during fasting in 26 ambulatory Type 1 (insulin-dependent) diabetic children without clinical signs of microangiopathy (age: 7-14 years; duration of disease: 3-14 years). Similar measurements were made in 28 healthy schoolchildren (age: 8-14 years). UPO4 V and CPO4/GFR were significantly enhanced in the diabetic children (p less than 0.001) and correlated with the degree of hyperglycaemia (p less than 0.005). TmPO4/GFR was significantly suppressed in the diabetic children (1.23 versus 1.73 mmol/l, p less than 0.001). This disturbance was neither related to changes in serum parathyroid hormone nor to growth hormone concentrations but was inversely correlated with the degree of hyperglycaemia (r = -0.61, p less than 0.001) and with tubular reabsorption of glucose (r = -0.53, p less than 0.01). In spite of the markedly lowered TmPO4/GFR in the diabetic subjects, the mean maximal (TmPO4) and absolute tubular phosphate reabsorption rates were equal to those of the 28 healthy subjects. Both in the diabetic and healthy subjects, these parameters were positively correlated with glomerular filtration rate which was significantly elevated in the diabetic children (138 versus 109 ml/min per 1.73 m2, p less than 0.01). The study demonstrates a dysfunction in tubular phosphate reabsorption in diabetic children which is related to glycaemic regulation.