Urinary ionic calcium and binding sites in normocalciuric idiopathic calcium urolithiasis

Total bindings sites, ionic calcium, and other crystalloids were measured in 41 normocalciuric patients with idopathic calcium urolithiasis and in 34 normocalciuric healthy subjects. Twenty-six stoneformers were treated with thiazide to determine the effect of the drug. The average total calcium excretion was higher in patients than in controls and patients receiving therapy. The fraction of total calcium ionized was higher in patients than in normal subjects; thiazide therapy did not seem to cause a decrease in this fraction in stoneformers. The 24-hr excretion of ionic calcium was equal in normal subjects and in patients receiving thiazide therapy, but was higher in patients without therapy. Normal subjects have a significantly higher concentration and total excretion of magnesium and citrate. Apparent binding constants for calcium were significantly different for all three groups. The concentration of total binding sites was lower in patients with and without therapy than in normal subjects; this was partly attributed to the higher urinary concentration of citrate in normal subjects. However, citrate accounted for less than 20 per cent of the total bindings sites in urine. There was no significant differential 24-hr excretion of binding sites. Measurement of the specific excreting pattern of binding sites on proteins, peptides, nucleotides, and amino acid may emerge with a characteristic pattern in patients with urolithiasis.