Ultrafiltrable Serum Citrate and the Relationship Between Serum and Urinary Citrate Results in Controls and Renal Calcium Stone Formers

Summary: The total and Ultrafiltrable citrate of serum were measured in healthy controls, and in patients with calcium-containing kidney stones classified into the various calciuria types (normocalciuria, renal, absorptive, resorptive hypercalciuria). The total citrate in two subgroups (normocalciuria, renal hypercalciuria) was significantly higher than in controls. Two independent analyses showed a mean Ultrafiltrable fraction of 0.86 (controls and stone formers, with the exception of resorptive hypercalciuria) and 0.95 (resorptive hypercalciuria), i.e. the calculated extent of binding of citrate to serum macromolecules (> 10000 Daltons). The differences in the fraction of free citrate between controls and renal stone formers are not sigriificant. The apparent mean association constants are (1/mol) 0.24 X l O2 (controls) and 0.29 X l O2 (noimocalciuria). There is a high correlation between the ultrafiltrable fraction and total citrate in the serum, and also between the ratlos urinary/serum creatinine and urinary/ serum total citrate, during a 2 h endogenous creatinine clearance in the morning (fast in g). These findings suggest that