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The analysis of 24-h urine is the gold standard to diagnose metabolic abnormalities in the stone-forming patient. However, urinary composition changes throughout the day and analyzing the whole 24-h urine may mask peaks of increased risk of crystallization.

To examine variations of stone-promoting and stone-inhibiting factors in urine using split 24-h samples from healthy and stone-forming children.

Urine was collected from 87 healthy and 26 stone-forming children using a split collection procedure (12-h daytime urine and 12-h overnight urine). Urine volume, pH, calcium (Ca), magnesium (Mg), phosphate (P), citrate (Cit), uric acid (Ur), and oxalate (Ox) were determined, and the Ca/Cit ratio was calculated.

The overnight urine samples in both groups had higher levels of P and Mg, lower volume, lower pH, and less citrate and uric acid. As can be seen in the table, higher …