[Diagnostic markers in calcium nephrolithiasis--current and traditional ideas with a new look]

About 80% of all renal stones contain calcium oxalate and/or calcium phosphate as their main crystalline components. The most important risk factors for increases in calcium oxalate crystallization are low urine volume, hyperoxaluria and hypocitraturia. Hypercalciuria, however, is of secondary importance as a cause of increased crystallization: whereas calcium and oxalate crystallize in a 1:1 ratio, the molar concentration ratio in urine amounts to about 10:1 in favor of calcium. Therefore, increases in urinary calcium will not be followed by a rise in crystallization as long as oxalate remains constant, whereas even the slightest increases in urinary oxalate immediately cause more crystals to precipitate. Thus, low calcium diet is not only unnecessary but is contraindicated since it may cause secondary hyperoxaluria (increased intestinal oxalate absorption) and osteopenia (negative calcium balance). On the other hand, overconsumption of animal protein (meat, poultry, fish) induces more pronounced hyperoxaluria and hypocitraturia and contributes to an overall negative calcium balance. It is, however, only by the interplay of "bad" dietary habits with underlying abnormalities such as up-regulation of calcitriol production, incomplete renal tubular acidosis or defective macromolecular crystallization inhibitors, that people become recurrent calcium renal stone formers.