Urinary excretion of calcium, uric acid and citrate in healthy children and adolescents

To obtain regional reference values for calcium, uric acid and citrate urinary excretion and establish a correlation between those excretions in 24-hour urine sample and single urine sample for their use in clinical practice. A hundred and twenty-five healthy children and adolescents were randomly chosen and submitted to the following protocol: clinical examination, biochemical analysis of blood, blood cell count, parathormone, 24-hour urine, fasting urine sample and stool test. The maximum value of calcium excretion in 24-hour urine was 3.75 mg/kg; in mg/dl of the glomerular filtration rate, it was 0.10; and for the calcium/creatinine (mg/dl) ratio in the fasting urine sample was 0.25. Positive correlation was observed between calcium excretion in the 24-hour urine and the fasting sample (mg/dl and mg/dl of glomerular filtration rate). The maximum values of uric acid excretion in 24-hour urine were 600, 450, and 320 mg and 13, 15 and 18 mg/kg for adolescents, school and preschool children, respectively; in mg/dl of glomerular filtration rate, in the fasting urine sample, it was 0.47. Positive correlation was observed for the uric acid excretion in 24-hour urine and fasting urine samples. The mean values for the citrate excretion in 24-hour urine were 1.6, 1.1 and 0.5 mmol for adolescents, school and preschool children, respectively; for citrate/creatinine ratio, in the fasting urine sample the mean value was 0.3. The calcium and uric acid excretion in 24-hour urine showed correlation with those in the fasting urine sample, which allows their use for metabolic diagnosis, population studies and follow-up of patients with hypercalciuria and hyperuricosuria without voiding control; the citrate/creatinine ratio in the fasting urine sample can be used for controlling patients with hypocitraturia.