Different estimates of the risk of calcium oxalate crystallization in urine.

Different mathematical expressions of urinary calcium, oxalate, magnesium, citrate and urine volume (V), formulated in order to reflect supersaturation with respect to calcium oxalate, were compared with the computer-calculated ion-activity product of calcium oxalate (APCaOx). A good correlation (r = 0.99) was demonstrated for the following two simplified relationships and APCaOx:Ca0.71 X Ox and (Ca0.71 X Ox)/V1.2. The correspondence between Ca/Mg quotients and APCaOx was generally less satisfactory.