Crystalluria in idiopathic recurrent calcium urolithiasis. Dependence on stone composition.

A retrospective study was done on the nature and degree of crystalluria in fasting and postprandial urine in patients with recurrent idiopathic calcium urolithiasis (RCU) for whom stone analysis was available. RCU was stratified into subgroups in accordance with stone analysis. The crystals were obtained and identified using a filter technique and polarization microscopy, respectively. Crystalluria score, relative saturation products (RSPs), and low-molecular-weight inhibitors were assessed. Calcium oxalate crystals were never observed in either male or female patients with stones composed exclusively of calcium oxalate, and only sporadically in patients with mixed stones (the additional component was calcium phosphate in most cases). Other crystalluria phases, such as amorphous calcium phosphate, a urate-containing phase, and a phase presenting as spherolytic particles, were slightly more frequent in patients with mixed stones. In contrast to crystalluria, RSPs and inhibitors differed in male and female patients, suggesting that crystalluria may not be under the exclusive control of these factors. The following conclusions were reached. (1) Calcium oxalate crystalluria is absent from RCU with pure calcium oxalate stones; hence, calcium oxalate crystalluria does not qualify as a diagnostic aid. (2) The co-existence of the isotropic phase and mixed stones may indicate that the formation of these concretions is characteristic for a major RCU subgroup. (3) On the basis of clinical chemistry and physicochemical data in urine and of crystalluria, it appears that the pathogenesis of RCU differs in male and female subjects.