Crystalluria determined by polarization microscopy

Summary A retrospective study was done on the nature and degree of crystalluria in spontaneously voided fasting and postprandial urine of patients with recurrent idiopathic calcium urolithiasis (RCU) divided into normocalciuria (20 males, 20 females) and hypercalciuria patients (20 males, 20 females), and controls (20 males, 20 females). The crystals were obtained using a filter technique and identified by microscopy. In addition, individual data, clinical chemistry variables and indices reflecting the risk of calcium phosphate and calcium oxalate crystallization were evaluated. In contrast to findings of other investigators of crystalluria we observed only a few crystals on the filters. The most frequently occurring phases were (in this order) a urate-containing phase (tentatively termed uric), an amorphous calcium phosphate phase (tentatively termed isotropic) and a phase of spheroid-like particles, not yet definitely characterized (tentatively termed spheroid). Calcium oxalate crystals were found only exceptionally. There was no relationship between the degree of calciuria (normo-versus hypercalciuric RCU) and crystalluria. Among RCU, males generally had a predominance of the isotropic, females of the spheroid phase, as compared with controls. Also, RCU females were generally obese, and their spheroid score and lean body mass correlated negatively and significantly. The calcium phosphate and calcium oxalate risk indices were always low in normal individuals, higher in RCU. Patients of both sexes with urinary stones had normal parathyroid gland function, but higher total calcium in fasting serum and higher urinary pH as compared with controls. From these data we concluded that (1) crystalluria is a regular finding in human urine, but is more pronounced in RCU; (2) in males, the isotropic phase, in terms of frequency and its score, may be causally related to the development of urolithiasis; (3) the spheroid phase, more frequently observed in RCU females, may reflect an as yet unknown metobolic disorder; (4) the rareness of calcium oxalate crystals despite a high calcium oxalate risk index suggests that such crystals may be adherent to upstream tissue.Part of this work was published as an abstract in Urol Res (1988) 16:235