[Microalbuminuria and tubular reabsorption of minerals in children with type 1 diabetes mellitus].

BACKGROUND

The most severe late complication of microangiopathic changes in diabetes mellitus type I (IDDM) is the diabetic nephropathy. The fully developed picture of diabetic nephropathy usually does not occur in children, however, original signs of altered renal functions may be present already.

OBJECTIVES

The study is aimed firstly at the detection of microalbuminuria and the relation between the amount of albumin urinary excretion and individual clinical indices such as age, degree of metabolic compensation, blood pressure. Secondly, the study's objective is to evaluate alterations in tubular reabsorption of minerals.

MATERIAL AND METHODS

1.) The occurrence of microalbuminuria has been detected on the basis of a four-year longitudinal clinical follow-up of 134 children (81 boys and 53 girls) with IDDM. Examinations which took place in regular twelve-month intervals were aimed at the investigation of the amount of albumin urinary excretion by means of radioimmunoanalysis in the collected twelve-hour night fraction of urine, simultaneous level of HbA1C and blood pressure values. The degree of the evaluated metabolic compensation during the first 5 years of diabetes occurrence was evaluated retrospectively and expressed as its mean value. 2.) 18 randomly selected patients and 12 controls were subdued to an examination of alterations in tubular reabsorption of minerals--sodium, calcium and phosphorus.

RESULTS

1.) On the basis of the amount of excreted albumin the children were divided into 3 groups. The first group (n = 105) consisted of children with normal albumin excretion, the second group (n = 13) represented children with transitory microalbuminuria, and the third group 16 (11.9%) were patients with persistent microalbuminuria. There was no significant difference observed in the degree of metabolic compensation between individual groups. At the end of investigation the diastolic blood pressure was significantly higher in the third group of children (76.1 +/- 0.9 and 75 +/- 1.9 or 82.8 +/- 1.8 mmHg, 0.001). A significant correlation was found between HbA1c, systolic and diastolic blood pressure and the amount of urinary excretion of albumin (p < 0.001). 2.) The investigation of tubular balance of minerals led to the detection of a significantly increased tubular reabsorption of sodium and calcium in children with IDDM (p < 0.001), whilst the urinary excretion of these ions did not increase. However, there were found significantly increased values of urinary phosphorus excretion (p < 0.001) with its value of tubular reabsorption remaining unaltered.

CONCLUSIONS

The alterations of glomerular functions is present already in the commencing stages of IDDM. The significance of examination of the amount of albumin urinary excretion augments after the twelfth year of age, during which the metabolic compensation becomes markedly deteriorated and the blood pressure elevates. Bad metabolic compensation with hyperglycaemia and glycosuria significantly influence tubular functions. This can represent the cause of the disturbed glomerulo-tubular balance which manifests itself by increased losses of phosphorus in children with IDDM. This fact can disturb osteogenesis in these patients. (Tab. 2, Fig. 3, Ref. 27.)