Post Void Residual Test: Meaning, Types, and Interpretation

Patients with bladder dysfunctions due to neurological, mechanical, or other causes often show signs of post-void residual (PVR).

Post-void residual describes the amount of urine left in the bladder after voluntary bladder emptying.

In the clinical context, post-void residual volume is a significant diagnostic tool, especially in urinary retention and other bladder-related medical conditions.

To effectively use PVR as a diagnostic tool, healthcare providers perform a post-void residual test to establish the extent of urinary retention.

With the results, they can also determine the clinical significance of PVR and apply the findings in treating bladder and urinary tract issues.

So, what is a post-void residual test, when is it required, how is it carried out, and when are the results clinically significant? You have answers for these and other questions in this article.

When you visit the restroom to empty your bladder, the natural situation that should happen is that all the urine flows out of your bladder through the urethra. However, if this does not happen and some urine stays in the bladder, a clinician will describe your situation as post-void residual urine.

A post-void residual test measures how much urine stays back in your bladder after voluntary bladder emptying.

Noticing that part of the urine remains in your bladder when you ease yourself may not be obvious. This is especially true if the residual volume is low or no presenting signs suggest a PVR situation.

So, what happens in this case?

The post void residual test can tell your provider if you are retaining urine post-void. But your doctor also needs to detect the need for a PVR test, which leads us to the question, when might your doctor consider a PVR test necessary?

Some patient situations create an obvious need for a post-void residual test. These include patients with postoperative urinary retention (POUR) and senior patients for whom urinary retention is a common issue.

In both cases, a doctor can order a post-void residue volume test for diagnostic purposes or as a precautionary measure.

However, individuals who do not fit into these two categories can also have PVR. In this case, a healthcare provider may order a post-void residue test for the following signs and symptoms:

The basic procedure for a post-void residual volume test consists of voiding your bladder as totally as possible just before the provider carries out the test.

Immediately after, the provider will perform one of these types of post void residual tests, depending on your doctor’s test request details.

Medics have long considered urethral catheterization the standard criterion for post-void residual testing. That’s because its accuracy level is deemed superior to other methods.
Urethral catheterization entails the introduction of a catheter into the bladder through the urethral opening.

Overall, the catheterization of male and female patients uses different techniques. However, the basics are similar.

Here’s a step-by-step procedure for urethral catheterization in post-void residual testing:

A bladder scanner, also known as a bedside bladder scanner is a portable ultrasound device that uses the 3-dimensional technique to measure urine volume in the bladder.

Medics prefer a PVR bladder scan in urinary residual testing because it is non-invasive and produces quick results.

To perform a post-void residual bladder scan:

Traditional bladder ultrasound uses a transvaginal approach in females or a transabdominal approach for both genders.

The intent is to record the bladder volume using a prolate ellipsoid formula (Width x Depth x Height x Correction Coefficient).

However, modern bladder ultrasound machines also make automatic bladder volume calculations.

The Transabdominal Postvoid Residue Ultrasound Test

The transabdominal postvoid residue test works in a similar manner as the portable bladder scanner described above. The ultrasound probe is passed on the suprapubic area over ultrasound gel while the patient lies in a supine position.

The provider passes the ultrasound probe in transverse and longitudinal turns and records the highest height, width, and depth measurements.

The transvaginal Postvoid Residual Ultrasound Test

The transvaginal postvoid residual urine volume test entails the insertion of a clean, gel-covered ultrasound probe into the vagina. The patient should lie in the supine position with raised knees.

Using the longitudinal probe position, the provider identifies the bladder on the ultrasound machine screen and measures the longest posterior length. The clinician then makes a 90° turn to record the width and depth measurements.

While doctors decide which type of PVR test is best for each patient case, they also prefer some types of post-void residue tests over others for their advantages. However, each has advantages and disadvantages, as shown in this PVR test comparison table.

It is worth noting that a perfect PVR test result is not an absolute necessity for medical decision-making. The presenting PVR test result is usually sufficient, even with a minimal ± discrepancy.

In all three types of postvoid residual tests, a medic determines if the bladder scan normal or abnormal levels are recorded. The results will inform consequent medical decisions: treatment, surgery, or catheterization.

Post-void residue urine volumes are either normal, acceptable, or high (indicative of urinary retention).

A universal consensus over what is a normal post void residual is elusive. Nonetheless, experts tend toward these tabled interpretations of normal PVR and what amount of residual urine is considered abnormal in adults and seniors.

In both adults and seniors, A PVR volume >500mL is considered abnormal and indicative of urinary retention. Experts recommend urethra catheterization in this case. Besides, medics often interpret such a PVR as a prognostic of Cauda Equina Syndrome, especially when related neurological signs and symptoms are present.

A bladder or ultrasound test that returns a urine volume of 1,500mL suggests urethra obstruction. Perform immediate urine draining in this case.

In children, a PVR of 20mL is taken to be abnormal. However, medics may interpret it differently depending on the child’s age.

A post-void residual test measures how much urine stays in the bladder after voluntary bladder emptying.

In the clinical context, post-void residual test volume is a core diagnostic tool for detecting urinary retention, especially in elderly patients and those from surgery. It can also detect other bladder-related diseases like neurologic bladder and Cauda Equina Syndrome.

Urethra catheterization, portable bladder scanners, and traditional ultrasounds are the three common types of PVR tests. Doctors will choose the appropriate type of post-void residual test based on each patient’s case.