High urinary excretion level of citrate and magnesium in children: potential etiology for the reduced incidence of pediatric urolithiasis.

It is well known that the incidence of calcium oxalate (CaOX) urolithiasis is much lower in children than in adults [2, 21]. One purpose of this study was to compare the inhibitory activity on CaOX crystal growth and nucleation of urine from children (ufC) with that of urine from adults (ufA). Another was to measure low molecular weight urinary substances related to CaOX lithiasis, including citrate and magnesium, which have been identified as stone inhibitors. The excretion volume per body weight of uric acid, phosphorus, magnesium and citrate was all significantly higher in 24-h ufC than in 24-h ufA, but that of calcium and oxalate was not. The growth inhibitory activities against CaOX crystals of ufC and ufA were measured in a whole urine system. The diameter of the crystals produced in this system was smaller for ufC (3.68 microm) than for ufA (4.66 microm). We also examined the metastable limit for CaOX with fresh spot urine, which was 3.15 mmol/l in ufC and 0.41 mmol/l in ufA. These results indicate that ufC has a more powerful inhibitory effect on CaOX crystal growth and nucleation than ufA. We also found that the excretion rate of citrate and magnesium in ufC was much higher than in ufA. We suggest that these two stone inhibitors are very likely to elevate the inhibitory activity of ufC against CaOX crystal growth and nucleation. The lower incidence of CaOX lithiasis in children might thus be partly attributed to citrate and magnesium.