Reference values for urinary calcium excretion and screening for hypercalciuria in children and adolescents

Hypercalciuria is of continuing interest as on of the risk factors for stone disease in children, but the definition, incidence and pathogenesis are controversial. Therefore reference values for the urinary calcium/creatinine (Ca/Cr) ratios were established in 564 healthy children aged 6–17.9 years during the fasting state (09.00 h) and in 236 of them also in the post-absorptive state about 2 h after lunch (14.00–16.00 h). The Ca/Cr ratios in both urine specimens were independent of age and sex, rendering it possible to determine a common normal range and to calculate centiles for Ca excretion in a large sample of healthy children and adolescents. To provide information about the incidence of hypercalciuria the Ca/Cr ratios of 1013 other apparently healthy children aged 6–17.9 years were measured during the post-absorptive state on two consecutive days. In 39 (3.8%) of them, 21 girls, and 18 boys, the Ca excretion was elevated in both urine specimens. Thirtysix of these children, all presenting without renal complaints, underwent further investigations to elucidate the possible mechanisms of the hypercalciuria.On the basis of the Ca/Cr concentration during the fasting state and the calciuric response to a standardised oral Ca tolerance test the children were subclassified into three groups: (1) Absorptive hypercalciuria (AH, n=12): Increased calciuric response to the Ca load, but normal fasting Ca/Cr; (2) Renal hypercalciuria (RH, n=8): Increased Ca/Cr after Ca load and during the fasting state; (3) Normal Ca excretion during the fasting state and after the Ca tolerance test, but increased sodium excretion (dietary hypercalciuria, DH, n=16).The serum prolactin levels were increased in AH, and the serum P and tubular P reabsorption rates were decreased in RH, while the parathyroid function and bone turnover were unimpaired in all groups.The study provides evidence that the measurement of Ca/Cr ratios in untimed random urine specimens during the post-absorptive state may be a reasonable screening test for elevated Ca excretion and that idiopathic hypercalciuria seems to be as prevalent in children as it is in adults.Abbreviations Ca/Cr calcium/creatinine - AH absorptive hypercalciuria - RH renal hypercalciuria - P inorganic phosphate - AP alkaline phosphatase activity - 25OHD 25-hydroxyvitamin D - iPTH immunoreactive parathyroid hormone - cAMP cyclic adenosine-3,5-monophosphate - GFR glomerular filtration rate - DH dietary hypercalciuria - OH-P total hydroxyproline