Validity of biochemical findings in the evaluation of patients with urolithiasis.

Urinary excretion of calcium, magnesium and oxalate was studied in 38 patients with urolithiasis on two different occasions, and there appeared to be a good correlation between the biochemical findings in the two samples. All values were expressed per mole of creatinine and it was furthermore demonstrated that the variation in creatinine excretion was considerably less than the variation in urine volume. The calcium/magnesium quotients were calculated in 113 2-hour fasting urine samples and 24-hour urine samples and a good correlation was obtained. Biochemical grouping of the patients was performed by means of the two sets of values and the result obtained was approximately the same in both cases.