An approximate estimate of the ion-activity product of calcium oxalate in rat urine

The objective of this report was to derive a simplified approximate estimate of the ion-activity product of calcium oxalate (AP_CaOx) in rat urine. The relative effect of each urine variable was assessed by means of iterative computerised approximation with the EQUIL2 program. A basic urine composition was chosen from literature and experimental data. The most pronounced influence on AP_CaOx was recorded for urinary calcium, oxalate, citrate, magnesium and volume. Based on these calculations, an AP(CaOx) index_RAT was formulated: \( \frac{{A \cdot Calcium^{{0.93}} \cdot Oxalate^{{0.96}} }} {{(Citrate + F)^{{0.60}} \cdot Magnesium^{{0.55}} \cdot Volume^{{0.99}} }} \). For a 24-h urine sample, factor A takes the value 4067 and factor F should be set to 0.015. Conclusion. A simplified approximate estimate of AP_CaOx was derived for rat urine. There was a reasonably good correspondence between AP(CaOx) index_RAT and AP_CaOx, as derived from EQUIL2 (r=0.890), provided the other urine variables do not deviate very much from that in the basic composition.