Obtain a collection container from your doctor or the laboratory and follow the directions you are given for collecting your samples. To preserve the substance to be tested, the container may need to be refrigerated during the entire collection process. After getting up in the morning, empty your bladder and discard that urine. Note the time. For the next 24 hours, save all urine voided in the container provided. When 24 hours are over, empty your bladder and ADD this urine to the container. Note the time. Bring all of the urine collected to the lab or doctor's office. If you miss collecting one or more voids, consult your doctor or the laboratory for further instructions.
The reason a 24-hour urine sample may be requested instead of a random urine sample is because amounts of various substances in the urine changes during the course of a day. By collecting all urine for 24 hours, the amount of the substance being measured in the urine can be averaged over the entire day and will give a better indication of what is going on in the body.