The urinary bladder is a sac-like structure that stores urine. When one goes to the restroom, the bladder should empty completely. However, at times some amount of urine remains in the bladder even after passing out the urine. Some volume of residual urine is usually present, but the problem arises when the residual amount is significant. Even after urinating, this amount of urine left in the bladder is known as pot-void residual (PVR) urine. A post-void residual test measures the amount of leftover urine in the bladder. This test may help the doctor to decide on a better treatment plan.
What Does Post-void Residual Urine Test Evaluate?
Post-void residual urine test evaluates:
Urine incontinence in men and women.
Problems with the passing of urine.
An enlarged prostate gland.
When Is the Post-void Residual Urine Test Indicated?
The physician can order a post-void residual urine test if one has urinary incontinence or retention symptoms. Urine incontinence could be due to:
A blockage in the urinary tract.
Side effects of certain medications.
Narrowing of the urethra- the tube through which urine passes out.
Neurogenic bladder-The nerves that carry the messages between the bladder and brain do not function properly.
Urinary tract infections (UTIs).
Damage to the kidneys.
Kidney or bladder stones.
How Does One Prepare for the Test?
Before proceeding with the procedure, the individual is asked to empty the bladder as completely as possible. The process begins immediately after passing urine.
What Is a Post-void Urine Test?
The post-void residual test is done by measuring the remaining amount of urine in the bladder immediately after passing urine. This test can be performed via ultrasound, bladder scan, or directly measuring the volume of urine drained by the catheter. The most crucial step before proceeding is immediately carrying out the procedure after urination. A delay of even five or ten minutes from bladder emptying to the post-void residual urine test likely causes a false reading of overestimating the post-void residual volume. The various tests and their procedure are:
1. Ultrasound - Standard ultrasound, also known as sonography, is a diagnostic imaging technique that uses sound waves to produce images of the internal organs or structures within the body. For example, it is used to picture the urinary bladder directly, either through the abdomen (transabdominal), belly, or vagina (transvaginal). It estimates the bladder’s volume using the ultrasound equipment’s internal volume calculations or mathematical equations. The transvaginal technique usually gives the correct estimation of the bladder volume.
Transabdominal Ultrasound - The individual is made to lie on their belly. Some gel is applied on the skin of the suprapubic area (the region below the belly button), and a transducer or a probe is moved around the place to get a clear picture of the bladder. Then sound waves are sent via the device through the abdomen. The waves are recorded and transformed into images on the computer screen. The pictures of the urinary bladder are recorded in both vertical and horizontal planes. Finally, the gel is wiped off the area. This procedure takes around thirty minutes to an hour.
Transvaginal Ultrasound - The transvaginal ultrasound is done to view the uterus, ovaries, fallopian tubes, cervix, and pelvis. The individual is made to lie on her back with her legs folded and knees bent. A clean probe is inserted into the vagina. The probe is usually covered with a condom and smeared with a get at the end. The procedure might be a little uncomfortable but not painful. The probe sends sound waves, which are recorded when they bounce back. The ultrasound equipment creates images of the bladder. Then the probe is gently rotated to view the other pelvic structures. The bladder images are recorded in a vertical plane.
Many ultrasound machines can automatically calculate the post-void residual urine volume from the measurements with calipers- a device that measures the dimensions of objects. In case of the unavailability of ultrasound calipers, the volume can be calculated with the help of a formula. The formula is post-void volume = length x width x height x 0.52.
Measurement calculated using this method is standard because it is fast and easy.
Limitations: The precise information of transabdominal ultrasound for determining the post-void urine volume is mixed, though many studies show high certainty with the use of transabdominal ultrasound. In comparison, some recent studies question their accuracy.
2. Portable Bladder Ultrasound Device (Bladder Scanner) - A portable bladder ultrasound device is a device that uses technology to digitally report the urine in the bladder and give 3D images of the urinary bladder. This is a non-invasive procedure. The individual is made to lie on their back. An ultrasound gel is applied to the suprapubic area (the area just below the navel). A transducer or probe is placed over the gel and moved around until the bladder is visible. Once the bladder is recognized, the volume of urine present in the bladder is recorded.
Limitations: Portable bladder ultrasound is not acceptable for use on individuals with severe abdominal scars, uterus prolapse, or pregnancy. In addition, a fluid-filled abdomen (ascites) due to conditions such as liver diseases, etc. might give a false result. However, some studies have found that portable bladder ultrasounds are much more precise than 2D ultrasound imaging techniques.
3. Urethral Catheterization - This technique directly measures the post-void residual urine volume and is considered the standard benchmark. Different techniques are required to insert a urethral catheter in males and females. However, the overall procedure remains the same. First, the individual is made to lie in a frog-leg position. Sterilized drapes cover the genitals exposing the urethral opening. For men, the penis is held straight up towards the ceiling, and in females, the skin folds around the vaginal orifice should be held and separated to expose the urethral opening. A lubricated catheter is inserted into the urethral orifice and observed for a return of urine to confirm its position within the bladder. Once the positioning is established, the catheter balloon is inflated with the help of saline. Then the bladder is entirely drained into a graduated or marked container, and the volume is measured. Once the bladder is fully emptied, the catheter is removed.
Limitations: Urethral catheterization can cause urethral trauma, the creation of faulty passage within the urethra, and unintended balloon inflation within the urethra. It can also lead to bacteria-led urinary tract infection if the procedure is not carried out with proper sanitization.
What Are the Complications of the Post-void Residual Urine Test?
The ultrasound techniques for determining the post-void residual volume do not pose grave risks. However, urethral or bladder catheterization has complications such as discomfort, developing urinary tract infection, injury, painful urination, or blood in the urine. Antibiotics can be prescribed in such cases.
Post-void residual urine test is a diagnostic procedure determining the cause of bladder urine retention. There are a few techniques to carry out the test. However, the procedures have limitations and complications that can be managed with medicines and hygiene.
Frequently Asked Questions