Calcium oxalate stone formation risk - a case of disturbed relative concentrations of urinary components

Although afflicted with stone formation, urolithiasis patients often present with normal renal excretions of lithogenic and inhibitory substances. In this study, crystal formation is not interpreted as the result of urinary excretions simply exceeding the static limits of normal ranges but rather as the consequence of relative combinations of such parameters which convert urine into becoming potentially lithogenic. Our model embraces different triplet combinations of fundamental urinary risk factors for calcium oxalate (CaOx) crystallization, to characterize different levels of urinary stone formation risk.

Urinalyses and BONN-Risk-Indices (BRI) were determined for CaOx patients under home conditions, after 1 week of hospitalization, and for healthy controls. The relative urinary concentrations and interdependences of, inter alia, free ionized Ca (Ca2+), bound Ca (Ca b), and oxalic acid (OA) were compared.

Three levels of CaOx formation risk can be distinguished: (I): low stone formation risk with an increase in (Ca2+) and concomitant decrease in (Ca b), while (OA) remains almost constant, BRI increases simultaneously; (II) moderate risk at (Ca2+)/(Ca b) approximately 1; and (III) high risk with decrease in (Ca2+)/(Ca b) and simultaneous increase in (OA).

The proposed approach of urinalysis interpretation allows complementary strategy of identification of patterns of disturbed urinary composites leading to calculus formation.