Kidney complications in primary hypercalciuria

Prevalence of hypercalciuria is markedly increased in patients with calcium kidney stones, and recently it has been demonstrated that the risk to produce stones is positively related with the levels of calcium excretion in general population. The stonepromoting effect of hypercalciuria depends on the unusually high calcium concentrations in urine and tubular fluid, which favor calcium salt precipitation. However, the specific role of calcium in the pathogenetic pathway leading to stone formation has not been elucidated and it is unclear whether initial events of this process develop in tubules or in papillary interstitium. Nephrocalcinosis occurs in the course of many hereditary or acquired disorders having hypercalciuria as the common alteration and can progressively damage kidney function. In spite of the relevance of hypercalciuria for nephrocalcinosis, the specific effect of calcium in its development is yet unknown. An increased frequency of hypercalciuria has also been recorded among patients with arterial hypertension. It has been hypothesized that a body calcium deficiency is induced by hypercalciuria and leads to the elevation of blood pressure. This may be true in a subgroup of patients, while hypercalciuria is likely to occur more commonly in patients with volumedependent hypertension. Irrespective of its possible causal role, hypercalciuria may predict individual susceptibility to stones, nephrocalcinosis or arterial hypertension. Measurement of 24 hour calcium excretion could become an instrument to identify subjects predisposed to these disorders.