Variations in urine composition during the day in patients with calcium oxalate stone disease.

The diurnal variations of urine composition with respect to calcium, magnesium, oxalate, citrate and inhibition of calcium oxalate crystal growth were studied in patients with recurrent calcium oxalate stone disease. There was considerable variation in the excretion of the different urine constituents with meal-related peaks, which was most pronounced for calcium. The highest concentration of calcium was observed before noon, and between 7 and 11 p.m. Oxalate concentration was highest between 6 and 10 a.m. Consequently, the highest levels of supersaturation were recorded between 6 and 10 a.m., and 6 and 10 p.m. The inhibition index was at the highest level during the first morning hours and could be important in counteracting crystal growth at that time. The risk of exceeding a theoretical formation product of calcium oxalate appeared to be low, with a 24-hour urine volume more than 2,000 ml.