Urine screening in outdoor volunteers: day versus night versus 24 hour collection

Urine constituents were measured in 12 healthy outdoor volunteers on four occasions within a month. Day, night, and 24 hour collection periods were compared. Measurements made on the four occasions did not differ. The amount of water, creatinine, electrolytes, proteins, and enzymes were higher during the day (up to three fold, p always less than 0.05), while equal amounts of amino acids were excreted in the day and the night period. A comparison of all values from all individuals for all four sampling occasions showed that the variation was lowest in the 24 hour samples. Relating the values to creatinine did not consistently reduce the variation. Twenty-four hour samples correlated better with the day than with the night samples. Day and night samples did not correlate. Twenty-four hour collection is superior to day or night collection in healthy outdoor volunteers. Based on the normal variation of values found in the present study, criteria for suspected kidney damage and therefore for the withdrawal of drugs in pharmacological studies can be defined for each collection period.