Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning) in a plastic bottle containing 1 g boric acid per liter of urine. Mix well. Screw the lid on securely. (It is acceptable to collect cortisol with a Hall preservative or without a preservative.)
