[New aspects of calcium metabolism in kidney calculus disease]

Recurrent calcium stone disease appears to be related to a high dietary intake of animal protein. The following mechanisms have been discussed to explain the relationship between dietary protein and calciuria: increased glomerular filtration rate (GFR), increased rate of sulphate excretion, acidosis-induced increase in ionised serum calcium ("filtered load") and decrease in tubular reabsorption, and mobilisation of bone mineral. Protein also diminishes urinary citrate. However, it has not been established in controlled trials whether a reduced dietary intake of protein diminishes the recurrence rate of renal stones. Determination of the normal range of urinary calcium is dependent on numerous variables: size; GFR; age; excretion of Na, Mg and Pi; dietary intake of Ca and protein; season. Ideally, all these variables should be evaluated. In many patients with recurrent stone formation hypercalciuria will be found. There is a consensus of opinion that intestinal Ca absorption is increased, but elevated frequency of a renal Ca leak has not been established. For patient management discrimination between absorptive and resorptive hypercalciuria is important; a simple test that can be performed as an outpatient procedure is proposed in order to make this distinction.