Have you had the sensation of keeping urine stored in the bladder after urinating? It is a frustrating sensation because you feel that you’re not done but cannot continue voiding.
Is it just an idea in your mind, or is it a real and measurable problem? Postvoid Residual Volume is one of the exams that will help you answer this question.
This exam is routinely done in patients with urinary tract obstruction. For example, in benign prostatic hyperplasia (BPH) and prostate cancer. It also has a role in diagnosing neurogenic bladder and other conditions.
In this article, we’re covering the topic of post-void residual volume. It is an explanation for those who feel urine stuck in the urinary bladder. And it is valuable information for anyone who needs a postvoid residual volume measurement and does not know what it is about.
What is postvoid residual?
Postvoid residual volume (PVR urine volume) is urine that stays in the bladder after voiding. The sensation of not eliminating all the urine in the bladder is real sometimes. Actually, there’s always a small volume left in the bladder, even in healthy people. But if you have a urinary obstruction, this volume is abnormally high (1).
To understand more precisely what is postvoid residual and how it works, let’s review the process of urinating:
- It all starts with a full bladder and the sensation of going to the bathroom.
- The bladder contracts every now and then, increasing the sensation temporarily. You can postpone voiding, and the sensation will come and go.
- As the bladder becomes full, the sensation becomes uncomfortable, and finally, you can’t resist the urge.
- When you’re voiding, the bladder wall contracts, and the bladder sphincter opens up. This releases the urine, which goes through the urethra directly to the outside.
- The first half of the urinary stream is very rapid because of the pressure in the bladder. Then, the stream is slower but steady until you’re done.
The voiding scheme mentioned above is what happens in healthy individuals, and the bladder’s urine pressure plays a significant role. The urine pressure is what triggers the need for voiding in the first place. The contraction of the bladder walls increases this pressure as the urine leaks out. We can also increase the abdominal pressure to push the urine to the outside. As the pressure reduces, the urine flow is slower, and it finally stops.
Postvoid residual is what is in the bladder after this struggle between the pressure inside and outside the body.
What happens when the postvoid residual volume is higher than normal?
- Something is obstructing the flow. It can be a kidney stone or an enlarged prostate. Either way, the source of the obstruction counters bladder pressure and slows down the urinary stream.
- In patients without urinary obstruction, the problem could be related to the bladder muscles. They contract to maintain the pressure uniformly throughout the voiding process. If they fail to contract, there won’t be enough bladder pressure to eliminate all of the urine.
- Sometimes there is a constant urge to void without actually having a full bladder. This is usually a nerve problem sending the wrong signals to the brain.
Postvoid residual volume measurements are helpful to detect and diagnose all of the conditions above. It is not only a reliable exam to see if you have post-void residual urine. It also measures how much residual urine volume retains in the bladder (1).
How to measure postvoid residual
If your doctor has ordered a postvoid residual measurement, you may wonder what it is about.
In simple words, this exam is a variation of the usual bladder ultrasound. A postvoid residual with catheterization is another alternative, but it is not commonly performed. In any case, this is a noninvasive evaluation. The goal is figuring out if you still have urine in the bladder after voiding. This leftover urine is measured and compared to the initial volume. There is no risk. And it doesn’t feel different from the usual ultrasound except that you need to start the exam with a full bladder and will need to empty your bladder in the process.
For this procedure, the doctor needs a voluntary void. In people who can’t cooperate with a voluntary void, a catheter method is an option. It may also work to get a sterile sample of urine in the process. Immediately after voiding, your doctor will measure the remaining urine in the bladder. Timing is crucial for the accuracy of the test. Only 10 minutes of delay can cause an increment of postvoid residual volume.
Three techniques are currently available to do the measurement (2):
Real-time or conventional ultrasound
A conventional ultrasound scan is enough to measure the postvoid residual volume in most cases. Healthcare providers can perform the scan trans-abdominally, placing the probe in the lower abdomen. They can also perform it transvaginally, inserting a special probe into the vagina. A transvaginal ultrasound is more accurate in obese individuals. It is also very useful if we want to measure low volumes of liquid in the bladder.
The technique requires three measurements to get an accurate volume of urine. They are a transverse measure for the width, a superior-inferior measure for the height, and an anteroposterior measure for the depth. In most ultrasound machines, the calculation is done automatically after completing three measurements. It calculates the volume automatically, but we can also do our own calculations with a volume formula.
Bladder scanner or portable bladder ultrasound
The bladder scanner is very similar to conventional ultrasound. But this device obtains a three-dimensional volume of the bladder. The exam is performed with ultrasound gel and placing the probe in the suprapubic area.
After pressing one button, the machine will do an automatic evaluation of the urine volume. It is often repeated to make sure that the volume is accurate. This type of exam is only appropriate for healthy and non-pregnant patients. Abdominal ascites, abdominal scars, or uterus prolapse cause false readings. But in healthy patients, measurements by bladder scanners are superior to the conventional ultrasound.
Urethral catheterization
This is the standard gold method to obtain the postvoid residual. In other words, it provides the most accurate reading. It does not depend on the patient’s collaboration to void or extra efforts to empty their bladder.
However, it is only done in select patients because it is often not necessary. It requires inserting a urethral catheter and positioning the catheter when placement confirms by inflating the balloon. Then, doctors allow the urine to drain by itself and remove the indwelling catheter.
This technique is accurate, but it involves a higher risk of urethral trauma, it is uncomfortable for the patient, and some people can get a urinary tract infection, even after using sterile instruments. According to studies, a bladder scan is performed in 45 seconds, and urethral catheterization is completed in 293 seconds. So, it is not as convenient and noninvasive as the methods above.
After getting the reading, it is compared by normal measures depending on the patient’s age.
In children, no more than 20 mL should be in the bladder after voiding. In adults, the remaining urine in the bladder should not exceed 50 mL. And in the elderly, we should have no more than 100 mL in the bladder. More than that would be considered abnormal.
What happens after the postvoid residual measurement?
Postvoid residual is a diagnostic tool, and after completing the measurement, you will listen to your doctor’s conclusion. If you got this exam, it is probably because your doctor wants to rule out a mechanical obstruction, a neurological disease of the bladder, a case of urinary retention due to medications or infections, or bladder dysfunction. This exam will only bring additional data to the table and may help diagnose several conditions (1):
Neurogenic diseases such as:
Cauda equina syndrome
There is swelling in the spinal cord’s lower section in this neurogenic problem. This affects the nerves and causes paralysis in the bladder. This diagnosis is suspected in patients with limb weakness or paralysis.
Diabetic bladder neuropathy
In diabetic patients, this could be causing urine retention. The disease affects nerves throughout the body. This often involves the bladder, the eyes, and the limbs.
Spinal cord injury or nerve impingement
After nerve impingement or a spinal cord injury, this also affects the bladder muscle function. Muscle spasms or insufficient muscle activity affect bladder pressure and cause retention.
Brain injuries (traumatic or vascular)
This diagnosis can be suspected in patients with cerebrovascular accidents or a vast region affected by motor and sensory problems.
Vitamin B12 deficiency
A vitamin deficiency can also compromise normal nerve function. This may happen to people with chronic malnutrition or vegans who do not consume vitamin B12 sources.
Multiple sclerosis or bladder denervation
The nerves are sometimes not injured but may have a thin myelin sheath. This structure surrounds the axon and serves as insulation to speed up nerve impulses. Bladder denervation happens in previous pelvic surgery and injury to the pelvic nerves and shows up as postoperative urinary retention.
Parkinson’s disease
This is a common cause of overactive bladder and other nerve conditions.
Mechanical problems such as:
- Benign prostatic hypertrophy: An increase in prostate volume is one of the most common causes of urinary obstruction in men. It is usually suspected in senior men because the incidence increases with age.
- Prostate cancer: It is also suspected in senior men. This exam does not distinguish between benign conditions of the prostate gland and prostate cancer.
- Kidney stones: In some cases, there’s a kidney stone interfering in the process of voiding. It can be located in the bladder or the urethra.
- Urethral strictures and hypospadias: The diagnosis of these conditions is easier to do by evaluating the patient directly. A postvoid residual is useful in these patients to assess the extent of the obstruction.
- Tumors or blood clots in the bladder: The obstruction source can be inside the bladder in the form of blood clots or a tumor. A postvoid residual won’t differentiate between benign tumors and cancer.
Inflammatory problems such as:
- Prostatitis: This is another prostate condition that links with obstructive symptoms. It is suspected in younger males with obstructive symptoms.
- Cystitis: A bladder infection may also change how this organ manages its own pressure, causing irritation and urinary retention.
- Herpes infections: This particular virus stays in the nerve tissue and causes damage to nerve structures and their associated organs. When the disease takes the bladder, it can cause nerve and motor problems.
How can I prevent problems with the urinary tract?
If you went through the list above, you probably didn’t know some of those conditions. There are many urinary tract problems out there and different ailments that trigger urinary symptoms.
We often neglect the urinary system until we experience problems with these critical organs. But you don’t need to experience pain or acute urinary retention to care about your bladder for the first time. Either if you’re healthy or having urinary symptoms, here’s a list of recommendations for you:
- Quit smoking because tobacco is an irritant of the urinary system (3)
- Avoid caffeine in beverages such as tea and coffee. They are also irritants of the urinary system (4)
- Maintain a healthy weight to reduce the load and the abdominal pressure on your bladder (5)
- Be more active and exercise a minimum of 30 minutes every day for 5 days a week (6)
- Stay hydrated and keep track of your water intake to clear your kidneys from stones. The average person is okay with 7 cups of water every day (7)
- Eat healthily, with many fruits and vegetables to maintain adequate bowel movements and reduce bladder pressure (8)
- Talk to your doctor if you have new or concerning urinary symptoms
Conclusion
People with lower urinary tract symptoms may experience urinary incontinence and a burning sensation when urinating. Another common problem is the sensation of incomplete bladder emptying. This problem usually arises from voiding dysfunction, which can have an obstructive or nerve-related source.
Bladder volume measurements through a postvoid residual will help determine if these patients have residual urine in the bladder after urinating.
This is a diagnostic tool that a doctor performs in a doctor’s office. It is similar to the regular ultrasound scan, except that you need to void and perform the test immediately after. Doctors use the standard ultrasound scanner or a special tool for bladder scanning. They may also use catheterization in patients who cannot collaborate.
The exam is very quick and only requires taking three measurements of your bladder after voiding. One for width, one for height, and one for depth. The scanner calculates the volume of urine using these measures, or we can do it ourselves with a formula.
After a postvoid residual, your doctor will take the exam and consider the symptoms you reported to give you a diagnostic appreciation and recommend treatment accordingly.
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