The diagnosis of hypercalciuria in children

Calcium loading tests were performed in 21 children with hypercalciuria, haematuria and/or nephrolithiasis and 10 control subjects. Comparisons of 24-h calcium excretion before and after loading were evaluated rather than fasting urinary calcium to urinary creatinine ratio. The differences in calcium excretion before and after loading clearly distinguished absorptive from renal hypercalciuria. A difference higher than 0.035 mmol/kg indicated absorptive hypercalciuria in 6 of 21 patients, whereas in the remaining 15 much lower differences indicated renal hypercalciuria. Resorptive hypercalciuria caused by low serum values of 25-hydroxyvitamin D was considered in 6 of the 15 patients with renal hypercalciuria. These patients had low values of phosphate reabsorption (TmP/GFR) and could be clearly separated by high values of calcium reabsorption (TmCa/GFR), in contrast to patients with renal hypercalciuria who had normal values of TmP/GFR and low values of TmCa/GFR. The correct treatment and prevention of nephrolithiasis caused by hypercalciuria in children should be based on accurate diagnosis; this can be achieved by using the calcium loading test described in this report.