ArticlesWhy the Doctor Asks for a Urine Sample
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(24-hour urine, urine volume)
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.
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.
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
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.
Twenty-four hour urine collection is a quick, simple diagnostic test that helps to diagnose problems with the kidneys. It is commonly performed to determine how much creatinine clears through the kidneys, but may also be used to measure protein, hormones, minerals, and other chemical compounds. Creatinine clearance testing provides information about kidney function.
Like all organs in the human body, the kidneys may be affected by various genetic and environmental circumstances, leading to kidney disease. Kidney (renal) disease may be temporarily or permanently damaging. Acute kidney disease has an abrupt onset and is potentially reversible. Chronic kidney disease progresses slowly over at least three months and can lead to permanent kidney damage. The causes, symptoms, treatments, and outcomes of acute and chronic kidney disease are different.
Conditions that can cause kidney disease include, but are not limited to, the following:
Diabetic nephropathy. A result of uncontrolled diabetes, which can cause permanent changes, leading to kidney damage
Hypertension. Abnormally high blood pressure, leading to permanent kidney damage
Lupus. A chronic inflammatory or autoimmune disease that can injure the kidneys, as well as the skin, joints, and nervous system
Frequent urinary tract infections
Prolonged urinary tract obstruction or blockage
Alport syndrome. An inherited disorder that causes deafness, progressive kidney damage, and eye defects
Nephrotic syndrome. A condition that has several different causes. Nephrotic syndrome is characterized by protein in the urine, low protein in the blood, high cholesterol levels, and tissue swelling.
Polycystic kidney disease. A genetic disorder characterized by the growth of numerous cysts filled with fluid in the kidneys
Cystinosis. An inherited disorder in which the amino acid cystine (a common protein-building compound) accumulates within specific cellular bodies of the kidney, known as lysosomes
Interstitial nephritis or pyelonephritis. An inflammation in the small internal structures in the kidney
Twenty-four hour urine collection may be performed along with other diagnostic procedures, such as cystometry and cystography.
There may be other reasons for your doctor to recommend 24-hour urine collection.
Twenty-four hour urine collection is a safe, noninvasive procedure that is usually done without direct assistance.
Certain factors or conditions may interfere with the accuracy of a 24-hour urine collection. These factors include, but are not limited to, the following:
Forgetting to collect some of your urine
Going beyond the 24-hour collection period and collecting excess urine
Losing urine from specimen container through spilling
Not keeping urine cold during collection period
Certain foods, such as coffee, tea, cocoa, bananas, citrus fruits, vanilla
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
Generally, no prior preparation, such as fasting or sedation, is required.
You may be instructed to start the collection at a specific time.
If possible, choose a 24-hour period when you will be at home so you do not have to transport your urine.
If you are pregnant or suspect that you may be pregnant, you should notify your doctor.
Notify your health care provider of all medications (prescription and over-the-counter) and herbal supplements that you are taking.
Based on your medical condition, your doctor may request other specific preparation.
Twenty-four hour urine collection may be performed on an outpatient basis or as part of your stay in the hospital. Procedures may vary depending on your condition and your doctor's practices.
Generally, 24-hour urine collection follows this process:
You will be given one or more containers for collecting and storing your urine. A brown plastic container is typically used to store the urine. A specimen pan or urinal may be used to collect the urine. You will need to transfer the urine from the collecting container to the storage container where it will be kept cold.
The 24-hour collection may begin at any time during the day after you urinate. However, it is common to start the collection the first thing in the morning. It is important to collect all urine in the following 24-hour period.
Do not save the urine from your first time urinating--the starting time. Flush this first specimen, but note the time. This will be the start time of the 24-hour collection.
All urine, after the first (flushed) specimen, will be saved, stored, and kept cold, either on ice or in a refrigerator, for the next 24 hours.
Try to urinate again at the same time, 24 hours after the start time, to finish the collection process, but if you cannot urinate at this time, it is not a problem.
Once the urine collection has been completed, the urine containers will be taken to the lab. If you are doing the urine collection at home, you will be given instructions on how and where to transport the specimen.
The procedure is concluded at this point. Depending on your specific medical condition, you may be asked to perform the test on several consecutive days.
Generally, there is no special type of care following 24-hour urine collection. However, your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.
The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.
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