Urinary inhibitors of crystallization in hypercalciuric children with hematuria and nephrolithiasis

Urinary inhibitors are suggested to play a significant role in reducing crystallization in calcium (Ca) stone former and idiopathic hypercalciuria (IH). Urinary inhibitors such as magnesium (Mg), citrate, and glycosaminoglycans (GAGs) were evaluated, as well as urinary Ca and creatinine (Cr), in IH children with nephrolithiasis (LIT) or with hematuria plus IH (HEM) and were compared with a control group. The mean 24-h urinary excretion of Mg was similar in all groups. However, the urine Ca/Mg ratio was significantly increased (P < 0.005) in LIT and HEM groups. A higher mean value for GAGs and citrate was found in the HEM group, but a very low level of GAGs (less than 60% of the normal value) and citrate (less than 30% of the normal value) was found in the LIT group. These data suggest that, despite a high urinary Ca excretion (3.6 +/- 0.1 mg/kg per day) in the HEM group, elevated urinary GAGs (32.0 +/- 1.0 mg/g Cr) and a normal urinary citrate (428.7 +/- 62.3 mg/24 h) excretion may prevent Ca crystallization and thus renal stones. In contrast, in the LIT group low urinary GAG (10.3 +/- 0.9 mg/g Cr) and citrate (235.2 +/- 52.3 mg/24 h) excretion may precipitate stone formation in the presence of a high urinary Ca excretion. Thus, it is reasonable to suggest that patients with hematuria and IH may not develop overt renal stone due to the presence of normal levels of renal stone inhibitors.