Weekend versus weekday urine collections in assessment of stone-formers.

Twenty-four-hour urine collections are an important part of the metabolic evaluation of stone-formers, but are difficult for patients at work. At weekends the results might be different. Forty-five stone-formers who worked at day jobs from Monday to Friday collected urine for 24 h on a normal working day and also on a Saturday or Sunday and the differences were evaluated. Average 24 h urine volume was higher on weekdays than at weekends. Calcium, oxalate, and uric acid excretion did not differ. These results imply an increased risk of crystalluria at the weekend. Therefore weekend collections are most likely to show abnormalities and should be acceptable to clinicians.