Proportional reduction of urine supersaturation during nephrolithiasis treatment

Purpose: During metabolic stone therapy, urine supersaturation decreases in proportion to pretreatment levels. We gauge the quantitative contribution of regression to the mean for reducing urine supersaturation from high pret reatment to lower values during therapy. Materials and Methods: The 24-hour urine supersaturations for calcium oxala te, calcium phosphate and uric acid were measured on 2 pretreatment and at least 1 treatment 24-hour collection for each of the 2,667 patients in 2 ne tworks and at a university based specialty clinic. Changes in supersaturati on between the first and second pretreatment collections were an estimate o f random change and compared to therapeutic changes. Results: Supersaturations decreased between the first and second pretreatme nt collections, proportional to the supersaturation in the first collection . However, the magnitude of this effect was minor compared to therapeutic c hanges. Also, mean change between pretreatment collections was 0, whereas m ean change with therapy was greater than 0 for all 3 supersaturations. Conclusions: Although regression to the mean can be detected, it cannot be responsible for the decrease in urine supersaturation with therapy or the f act that the decrease is proportional to pretreatment mean supersaturation. The mechanisms responsible for proportional reduction remain to be clarifi ed.