Standardized estimate of the ion activity product of calcium oxalate in urine from renal stone formers.

An estimate of the ion activity product of calcium oxalate [AP(CaOx) index(s)] was calculated for a standardized 24-hour urine volume of 1,500 ml. AP(CaOx) index(s) was higher in stone formers than in normal subjects and higher in men than women. There was a good correlation between AP(CaOx) index(s) and our previously described CaOx risk index. AP(CaOx) index(s) might be particularly useful for comparison of different groups of patients as well as for comparison of men and women. It can be assumed that such an index will be very useful for evaluation of patients with short-term urine collections.