What Is a 24-Hour Urine Test?

My doctor just ordered a 24-hour urine test. Why is it necessary to collect my urine for 24 hours, when I normally just provide a single urine sample at the doctor's office?

A single sample of urine is normally used to determine whether there are increased amounts of specific substances in your urine, such as glucose, red blood cells, white blood cells, or protein. The urinalysis is a "snapshot" assessment of your urine at one point in time. The urinalysis is a valuable screening tool for urinary tract infections, kidneys diseases, and other conditions.

However, sometimes doctors need to know how much urine your body is producing in a day or how much of a particular substance (for example, protein, aldosterone, sodium, potassium, or urea nitrogen) is eliminated in a day. A single-specimen urinalysis cannot provide this information, so patients are instructed to collect all their urine produced in a 24-hour period. A special container is provided for this purpose, which is returned to the laboratory after you have finished the urine collection at home.

For example, a doctor will order a 24-hour urine collection for creatinine in order to calculate how well a patient's kidneys are functioning. A doctor may also order a 24-hour urine collection for a hormone (5-HIAA) in order to exclude carcinoid syndrome. Today, I (Dr. Lee) ordered a 24-hour urine collection to measure a patient's rate or urine excretion of copper to exclude Wilson's disease (a genetic disorder that can cause excessive copper accumulation in the body and cause hepatitis and brain damage).