Urinary calcium excretion in healthy children and children with primary monosymptomatic nocturnal enuresis

Purpose: We investigated the role of urinary Ca excretion in monosymptomatic nocturnal enuresis, and defined normality and intra-individual variability in Ca excretion in healthy children. Materials and Methods: We included 46 Danish children with desmopressin resistant nocturnal enuresis and 96 healthy controls. We performed fractional urine collections at home during 2 days in controls or during hospitalization in children with enuresis. Urine volume, osmolality, and Ca and creatinine measurements were performed and Ca-to-creatinine ratios were calculated and compared between groups. Based on nocturnal urine output children with enuresis were characterized as having polyuria (nocturnal urine volume greater than 130% of expected bladder capacity) or not having polyuria. Results: We did not find any differences in controls compared with children with enuresis who did not and did have nocturnal polyuria in daytime Ca excretion (mean +/- SE 0.121 +/- 0.012, 0.078 +/- 0.014 and 0.095 +/- 0.020 mg/mg creatinine), nighttime Ca excretion (0. 115 +/- 0.011, 0.092 +/- 0.019 and 0. 139 +/- 0.029 mg/mg creatinine) or 24-hour Ca excretion (0. 118 +/- 0.011, 0.083 +/- 0.014 and 0.106 +/- 0.020 mg/mg creatinine, respectively). Urinary Ca excretion was not influenced by patient age, sex or body weight and, furthermore, we did not find evidence of diurnal variation. However, we observed considerable intraindividual variability in diurnal, nocturnal and total 24-hour urinary Ca-to-creatinine ratios. Conclusions: These observations contradict several previous reports and speculations on a role of Ca in the pathogenesis of nocturnal enuresis.