Factors Influencing the Course of Calcium Oxalate Stone Disease

Abstract

Objective: To assess the influence of previous stone formation, urine and stone composition on the further course of the disease in recurrent calcium stone formers without pharmacological treatment. Method: The course of the disease was analysed during a prospective follow-up period by means of Kaplan-Meier estimates. At the start of follow-up the patients were subgrouped with regard to their previous history of stone formation expressed as stone age index (SAI = 100 × number of stones/age), urine composition, stone composition, and sex. In 223 of the patients was it possible to calculate AP(CaOx) index_s, a standardized estimate of the ion-activity product of calcium oxalate. Results: The 446 patients (329 men, 117 women) who were considered representative of an average population of recurrent calcium stone formers, had a 5-year recurrence risk of approximately 50%. Patients with an SAI <2 had a lower recurrence risk than those with an SAI >2 and a corresponding difference was recorded between patients with SAI levels <5 and >5. Furthermore, female patients had a lower risk of new stone formation than male patients. Patients with an AP(CaOx) index_s of 1.5 or more had a significantly higher recurrence risk than those with a lower index, a difference that was most pronounced in female stone formers. A slightly higher risk of recurrent stone formation during the follow-up period could also be related to the presence of calcium phosphate in the stone, a high AP(CaP) index_s (a standardized estimate of the ion-activity product of calcium phosphate) and a low concentration of citrate. Conclusion: AP(CaOx) index_s and SAI were the most obvious predictors of the recurrence risk and these two variables, together with information on the sex distribution, might be useful for deriving an expected recurrence risk at a defined point of time in a group of recurrent stone formers. Such an estimate can be valuable for conclusions on the efficacy of different stone-preventive treatments when an appropriate control group is lacking.