24-Hour Urine Collection

(24-hour urine, urine volume)

Procedure overview

What is a 24-hour urine collection?

A 24-hour urine collection is a simple diagnostic procedure that measures the components of urine. The test is noninvasive (the skin is not pierced), and is used to assess kidney (renal) function.

Twenty-four hour urine collection is performed by collecting a person's urine in a special container over a 24-hour period. The container must be kept cool during this time until it is returned to the lab for analysis.

Urine consists of water and dissolved chemicals such as sodium, potassium, urea (formed from protein breakdown), and creatinine (formed from muscle breakdown), along with other chemical compounds. Normally, urine contains specific amounts of these waste products. If these amounts are not within a normal range, or if other substances are present, it may be an indication of a particular disease or condition. The results of a 24-hour urine collection may provide information to help your doctor make or confirm a diagnosis.

Related procedures that may be used to diagnose kidney disease include kidney ultrasound, kidney scan, kidney biopsy, and renal arteriogram.

How does the urinary system work?

The body takes nutrients from food and converts them to energy. After the body has taken the nutrients it needs from the food, waste products are left behind in the bowel and blood.

The urinary system keeps chemicals, such as potassium, sodium, and water in balance, allowing the body to function properly. The kidneys also remove protein waste, called urea, from the blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

Other important functions of the kidneys include blood pressure regulation, and the production of erythropoietin, which controls red blood cell development in the bone marrow.

Urinary system parts and their functions:

  • Two kidneys. A pair of purplish-brown organs located below the ribs toward the middle of the back. Their function is to remove liquid waste from the blood in the form of urine, keep a stable balance of salts and other substances in the blood, and produce erythropoietin, a hormone that aids in the formation of red blood cells.

    The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

  • Two ureters. Narrow tubes that carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.

  • Bladder. A triangle-shaped, hollow organ located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.

  • Two sphincter muscles. Circular muscles that help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder

  • Nerves in the bladder. Alert a person when it is time to urinate, or empty the bladder

  • Urethra. The tube that allows urine to pass outside the body

Facts about urine:

  • Adults pass about a quart and a half of urine each day, depending on the fluids and foods consumed.

  • The volume of urine formed at night is about half that formed in the daytime.

  • Normal urine is sterile. It contains fluids, salts, and waste products, but it is free of bacteria, viruses, and fungi.

  • The tissues of the bladder are isolated from urine and toxic substances by a coating that discourages bacteria from attaching and growing on the bladder wall.



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