Urinary inhibitors of crystallization in hypercalciuric children with hematuria and nephrolithiasis

Abstract

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.

Biochemical risk factors for stone formation in a Scottish paediatric hospital population

“…22 Low levels of urinary citrate therefore may be a significant cause of renal stones. 23 Our observation of hypocitraturia in paediatric stone-formers has previously been described by several authors, 3,4,7,8 although others, 5,10,24 have failed to show a difference in citrate excretion compared with controls.…”

The relationship of magnesium intake to serum and urinary calcium and magnesium levels in Trinidadian stone formers

“…In contrast, a low incidence of calcium oxalate stones in Japanese children has been attributed to a high excretion rate of magnesium and citrate 18 . As a corollary to this, an increased urinary calcium to magnesium ratio was demonstrated in a group of affected children in a Brazilian study, although in that series the 24 h Mg excretion did not differ from controls 19 . In the present study, our patients showed a similar increase in the ratio of urinary calcium to magnesium, not accompanied by any decrease in urinary magnesium excretion.…”

Evaluation of lithogenic elements in urine of healthy newborns

“…We observed that females had higher excretion of citrate and K than males, suggesting that female infants may be more protected than males, as in the adult population [22]. It was interesting to observe that newborns fed with breast milk had a lower excretion of Ca, UrAc, and Ox than those fed with artificial milk.…”

“…In contrast, there are few reports concerning urinary citrate excretion. Perrone et al [22] showed low urinary citrate excretion in renal stone-forming children. They observed that these patients presented lower urinary citrate excretion compared with non-stone formers, suggesting that low urinary citrate excretion could be involved in the genesis of stone formation.…”