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: [formula; see text]. 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.