Estimation of the concentration of urinary ionic calcium and its clinical role in urolithiasis

The concentration of urinary ionic calcium was estimated using an ion-selective electrode and ion analyzer for healthy controls and patients with calcium urolithiasis. The following results were obtained: 1) After calculating the ionic strength and calibrating the standard solutions of ionic calcium in each urine, the urinary ionic calcium was estimated using an ion-selective electrode and ion analyzer. The reproducibility and accuracy of the value of urinary ionic calcium were satisfactory. 2) There was a significant correlation between the concentration of urinary ionic calcium and the total calcium excretion. Although the percentage of ionic calcium did not show any correlations among the total calcium, oxalate and urinary pH, it had an inverse relation to urinary citrate and phosphate. 3) In calcium stone formers, the excretion of ionic calcium was higher than in healthy controls significantly. 4) In hypercalciuric calcium stone formers, the concentrations and excretions of total and ionic calcium were significantly higher than in normocalciuric calcium stone formers. However, the percentage of ionic calcium was not different. 5) When the patients were treated with citrate orally, the excretion of urinary citrate was increased, and the excretion of ionic calcium and the percentage for total calcium were decreased significantly. There were significant reductions of ionic calcium in the urine after oral administration of rice-bran. 6) The estimation of urinary ionic calcium might be important to evaluate the urinary risk in recurrent calcium stone, and to estimate the effects of the preventive treatments for its recurrence.