Bladder Ultrasound in Ajax: Post-Void Residual Explained

Why would anyone ask you to arrive with a full bladder, scan it, send you to the washroom, and then scan it again a few minutes later? If you have been booked for a bladder ultrasound with a post-void residual measurement, that is more or less what will happen, and it can seem a little odd until you know what the second set of pictures is for.

The short answer is that your health-care provider wants to know two things: what your bladder looks like when it is full, and how well it empties. The second part is what “post-void residual” refers to. This article explains the term in plain language, the common reasons a provider asks for it, how the exam runs at our clinic in Ajax, and a few practical tips that help the measurement come out as accurate as possible.

Decoding the name

Medical terms are often just ordinary ideas in formal clothing, and this one is a good example.

• Post means after.
• Void is the clinical word for emptying your bladder, in other words urinating.
• Residual means what is left over.

Put together, a post-void residual, often shortened to PVR, is the amount of urine that remains in your bladder after you have been to the washroom. Most people do not empty their bladder perfectly every single time, so a small amount left behind can be quite ordinary. What your provider is interested in is whether the amount is larger than expected, and whether it fits with the symptoms that led to the test.

Ultrasound is well suited to answering that question. Urine is fluid, and fluid shows up clearly on an ultrasound screen as a dark, well-defined space. By measuring the bladder in several directions, the sonographer can estimate its volume without any needles, catheters or radiation.

Why a provider might ask for it

A post-void residual measurement is usually one piece of a larger assessment. Your provider will have their own reasons, written on your requisition, but some common situations include:

• Needing to urinate very often, or waking at night to go
• A weak or stop-and-start stream
• Having to strain, or feeling that the bladder never fully empties
• Repeated urinary tract infections
• Leaking urine, especially if it happens with a constant feeling of fullness
• Monitoring a known condition that can affect bladder emptying, such as an enlarged prostate
• Checking how things are going after a procedure or a change in medication, since some medicines can affect how the bladder works

None of these automatically point to one particular cause. Bladder symptoms can come from many sources, some minor and some that need closer attention, which is exactly why a measurement helps. It gives your provider an objective number to put alongside what you have described.

The two-part scan, step by step

The exam is simple, but it does have a rhythm to it. Here is how a typical bladder ultrasound with a post-void residual measurement unfolds.

Part one: the full bladder

You lie on your back on the examination bed, and the lower part of your abdomen, just above the pubic bone, is uncovered. The sonographer applies warm or room-temperature gel and moves the transducer across the area. You will feel light pressure, which can be a little more noticeable when your bladder is full, but it should not be painful.

With the bladder full, its wall is stretched and smooth, and its outline is easy to see. The sonographer records images in two directions and takes measurements. The report may describe the shape of the bladder, the appearance of its wall, and anything visible inside it.

Part two: the washroom break

Next, you will be asked to empty your bladder. This is a genuine part of the test, not an interruption, so take your time and empty as completely as you comfortably can.

Part three: the after picture

You return to the room straight away, lie back down, and the sonographer scans the bladder again. This second set of measurements is the post-void residual. Speed matters here, because the kidneys produce urine continuously and the bladder begins to refill as soon as you leave the washroom. A prompt rescan gives the truest picture of what was left behind.

The whole exam is usually brief, though the time depends on what else your provider has requested.

Preparing for the appointment

For the first images to be useful, the bladder needs to contain enough urine to be clearly seen and measured. Exactly how full, and how to get there, depends on your exam and anything else being scanned on the same visit. Our team will confirm your preparation instructions when you book, and they are the instructions to follow.

If you have had a pelvic ultrasound before, the idea of drinking water ahead of time will be familiar. We have explained the reasons behind a full bladder, and how to time the water so it is manageable rather than miserable, in our article on why a full bladder matters for pelvic ultrasound. The same common sense applies here.

A few points specific to a residual measurement:

1. Tell the clinic about your symptoms when you book. If you struggle to hold urine for long, or you find it difficult to get started once you are in the washroom, the team can talk through what is practical for you.
2. Ask before changing any medication. Some medicines affect the bladder, but do not stop or skip anything on your own. If you have questions about medication timing, speak with your health-care provider.
3. Bring your health card and requisition, as you would for any ultrasound.
4. Note anything unusual on the day. If you have recently had an infection, a catheter, or a procedure, mention it at check-in.

Tips for an honest emptying

The number recorded after you void is only meaningful if it reflects how your bladder usually empties. A rushed or tense visit to the washroom can leave more urine behind than normal, while some people unconsciously do extra things to get every last drop out. Either can nudge the result in one direction.

These suggestions help:

• Go as you normally would. If you usually sit, sit. If you usually stand, stand. There is no special technique to use.
• Do not rush. The sonographer would rather wait an extra minute than have you hurry.
• Try not to strain or push unless that is genuinely how you always urinate. If it is, say so afterwards.
• Mention double voiding. Some people go, wait a moment, and go again. If you did that, let the sonographer know, since it is useful context.
• Speak up if you could not go, or if you only managed a small amount. It happens, especially in an unfamiliar washroom, and it is far better to say so than to leave the sonographer guessing.

Feeling self-conscious about this part of the exam is common. Sonographers do these scans routinely, and nobody is listening at the door.

What the scan can and cannot tell your provider

A bladder ultrasound gives useful information, but it is one tool among several.

What it can show

• An estimate of the bladder’s volume before and after you urinate
• The outline and wall of the bladder
• Some findings inside the bladder, depending on what is present
• In some cases, other structures your provider has asked about on the same requisition

Bladder imaging is sometimes requested together with the kidneys, because the two are part of the same system. If your requisition includes both, our article on kidney and gallbladder ultrasound describes what the kidney portion involves, including the positions you may be asked to take.

What it does not show

An ultrasound does not measure how forcefully urine flows, the pressures inside the bladder, or how well the nerves and muscles are coordinating. If your provider needs that kind of information, they may arrange other tests. A single residual measurement is also a snapshot of one moment. Bladder emptying can vary from day to day, so your provider will interpret the number in the context of your symptoms and history, and may sometimes suggest a repeat.

When this is not a booking matter

A bladder ultrasound is a planned, non-urgent test at a community imaging clinic. Some situations need emergency care instead. If you suddenly cannot urinate at all, especially with a painful, swollen lower abdomen, call 911 or go to the nearest emergency department. The same applies if you have urinary symptoms together with a high fever, severe back or side pain, confusion, or a general feeling of being very unwell. Do not wait for an imaging appointment in these situations.

For new or changing symptoms that are less severe, contact your health-care provider, who can decide whether the timing of your scan needs to change.

Common questions

Is the scan uncomfortable?

Most people find it easy. The pressure of the transducer on a full bladder can create a stronger urge to go, but that part is short, and relief is only a few minutes away.

Can I have it done on a Saturday?

Our Ajax clinic is open Saturdays from 8:00am to 3:30pm as well as weekdays from 9:00am to 5:00pm. Call to ask about appointment availability for your exam.

Who gets the results?

Like other diagnostic ultrasound exams, the report goes to the provider who ordered it. We describe that path in more detail in our article on how imaging results reach your doctor.

Do I need to bring someone with me?

It is not required, but you are welcome to bring a support person if that helps you feel more at ease.

Booking a bladder ultrasound in Ajax

Rossland Diagnostic Clinic is at Unit 102, 300 Rossland Road East, with free parking and ground-floor access, which is convenient for patients coming from across Ajax, Pickering and Whitby. You can learn more about our ultrasound services, call us at 905-426-3111 with your requisition in hand, or request an appointment online and our team will be in touch to confirm a time and go over your preparation.