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(Urine Flow Studies, Urine Flow Test, Urodynamic Studies)
What is uroflowmetry?
Uroflowmetry is a simple, diagnostic screening procedure used to calculate the flow rate of urine over time. The test is noninvasive (the skin is not pierced), and may be used to assess bladder and sphincter function.
Uroflowmetry is performed by having a person urinate into a special funnel that is connected to a measuring instrument. The measuring instrument calculates the amount of urine, rate of flow in seconds, and length of time until completion of the void. This information is converted into a graph and interpreted by a doctor. The information helps evaluate function of the lower urinary tract or help determine if there is an obstruction of normal urine outflow.
During normal urination, the initial urine stream starts slowly but almost immediately speeds up until the bladder is nearly empty. The urine flow then slows again until the bladder is empty. In persons with a urinary tract obstruction, this pattern of flow is altered, and increases and decreases more gradually. The uroflowmeter graphs this information, taking into account the person’s gender and age. Depending on the results of the procedure, other tests may be recommended by your doctor.
Other related procedures that may be used to diagnose urinary outflow obstruction or lower urinary tract dysfunction include cystometry, cystography, retrograde cystography, and cystoscopy. Please see these procedures for additional information.
How does the urinary system work?
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The body takes nutrients from food and converts them to energy. After the body has taken the food that it needs, waste products are left behind in the bowel and in the blood.
The urinary system keeps the chemicals, such as potassium and sodium, and water in balance, and removes a type of 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.
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 the formation of red blood cells. The kidneys also help to regulate blood pressure.
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.
Uroflowmetry is a quick, simple diagnostic screening test that provides valuable feedback about the health of the lower urinary tract. It is commonly performed to determine if there is obstruction to normal urine outflow. Medical conditions that can alter the normal flow of urine include, but are not limited to, the following:
- Benign prostatic hypertrophy (BPH)--a benign enlargement of the prostate gland that usually occurs in men over age 50. Enlargement of the prostate interferes with normal passage of urine from the bladder. If left untreated, the enlarged prostate can obstruct the bladder completely.
- Cancer of the prostate, or bladder tumor
- Urinary incontinence--involuntary release of urine from the bladder
- Urinary blockage--obstruction of the urinary tract can occur for many reasons along any part of the urinary tract from kidneys to urethra. Urinary obstruction can lead to a backflow of urine causing infection, scarring, or kidney failure if untreated.
- Neurogenic bladder dysfunction--improper function of the bladder due to an alteration in the nervous system such as a spinal cord lesion or injury
- Frequent urinary tract infections (UTI’s)
Uroflowmetry may be performed in conjunction with other diagnostic procedures, such as cystometry and cystography.
There may be other reasons for your doctor to recommend uroflowmetry.
Because uroflowmetry is a noninvasive procedure, it is safe for most persons. The test is usually done in privacy to ensure that the person voids in a natural setting.
There may be risks depending upon your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may interfere with the accuracy of uroflowmetry. These factors include, but are not limited to, the following:
- Straining with urination
- Body movement during urination
- Certain medications that affect bladder and sphincter muscle tone
- 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 drink about four glasses of water several hours before the test is performed to ensure that your bladder is full. In addition, you should not empty your bladder before arriving for the procedure.
- If you are pregnant or suspect that you are pregnant, you should notify your doctor.
- Notify your doctor 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.
Uroflowmetry 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, uroflowmetry follows this process:
- You will be taken into the procedure area and instructed how to use the uroflowmetry device.
- When you are ready to urinate, you will press the flowmeter start button and count for five seconds before beginning urination.
- You will begin to urinate into the funnel device that is attached to the regular commode. The flowmeter will record information as you are urinating.
- You should not push or strain as you urinate. You should remain as still as possible.
- When you have finished urinating, you will count for five seconds and press the flowmeter button again.
- You should not put any toilet paper into the funnel device.
- The procedure will be 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 uroflowmetry. However, your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.