Background Idiopathic Hypercalciuria (IH) has been associated with decreased bone density up to 30% of the children.

Aims To determine the concentrations of cytokines osteoprotegerin (OPG) and sRANKL and other biochemical indices of bone metabolism in children with IH.

Methods In 31 children of median age 6.3 years (range 2.2–16.4) with IH OPG, sRANKL, 25(OH)D, 1,25(OH)₂D, PTH, Ca, Pi, osteocalcin, ALP and CTx-Crosslaps were determined in serum and Ca/Cr, oxalate/Cr and citrate/Cr in urine. Times of study were at diagnosis and after 3 months of salt free and adequate Ca diet. Height and BMI z-score were assessed. Clinically healthy children (n = 35) matched for age/sex and season were used as controls (median 7.8 years, range 1.8–16.3).

Results Although urinary Ca excretion (24 hCa and UCa/UCr) decreased at 3 mo (p < 0.05 and p < 0.01) on average it had not reached control values (p < 0.0001, p = 0.0004). No significant differences were found for urine excretion of citrate and oxalate or for serum Ca, Pi, 25OHD, 1,25(OH)₂D, PTH, osteocalcin, ALP, OPG, sRANKL and sRANKL/OPG ratio in patients before and after diet or compared to controls. Only serum concentrations of CTx-Crosslaps were significantly higher in both patient samples (p < 0.02, p < 0.05) than controls. The BMI z-score was lower in patients than controls (p = 0.016), but height did not differ.

Conclusion Although serum OPG/sRANKL and osteocalcin were not different in children with IH, the higher serum CTx-Crosslaps levels (bone resorption index) may suggest bone turnover uncoupling with an autocrine role of the above cytokines.