A proposed method for approximate estimates of the ion-activity products of calcium oxalate and calcium phosphate in spot-urine samples or in urine samples collected during less well defined periods of time

摘要

The purpose of this study is to derive approximate estimates of ion-activity products of CaOx (AP(CaOx)) and CaP (AP(CaP)) useful for spot urine or other less well defined short-term urine collections. In accordance with previously applied and described principles for estimating ion-activity products, the intention was to derive simplified estimates of AP(CaOx)(CONC) and AP(CaP)(CONC) by using urine concentrations of the most important determinants of AP(CaOx) and AP(CaP). A comparison thus was made between estimates derived in that manner and AP(CaOx) index and AP(CaP) index obtained from calculations based on analysis of 24 h urine samples. The best fit between estimates of AP(CaOx) index in 24 h urine and AP(CaOx) index(CONC) was obtained with the following formula (r = 0.99; p = 0.0000): AP(CaOx)index(CONC) = 2.09xcCa(0.84)xcOx/cCit(0.22)xcMg(0.12). The corresponding formula for AP (CaP) index(CONC) was derived from comparison with the corresponding calculations of AP(CaP) index in 24 h urine (r = 0.91; p = 0.0000): AP(CaP)index(CONC) = 0.432xcCa(1.07)xcP(0.70)x(pH-4.5)(6.8)/cCit(0.20). The proposed simplified formulas enable calculation of approximate estimates of AP(CaOx) and AP(CaP) in spot-urine samples or any kind of urine collection for which duration of the collection period is less well known and by using the concentrations (c) of the variables in mmol/L in the two formulas.