Post Void Residual Urine and Prostate Volume on Ultrasound

Post void residual urine (PVR) is the amount left in your bladder straight after you pass urine, measured by ultrasound in millilitres. A small residual is common and often unimportant; a large one, especially in the range of a couple of hundred millilitres, suggests the bladder is not emptying well and needs a doctor’s attention. Prostate volume, the other number on the page, tells you the gland’s size, and size alone matches symptoms less closely than most men expect.

What is post void residual urine, and why is it measured?

Picture a balloon. Now give it a tap at the bottom. The prostate wraps around that tap like a ring. As many men age, the prostate grows (benign prostatic hyperplasia, BPH) and can squeeze the outflow. The bladder muscle pushes harder for years, and some men eventually reach a point where it can’t push the last of the urine out.

PVR measures that leftover. Simple idea. After you pass urine, the sonographer places the probe on your lower belly and calculates the volume still in the bladder. An international teaching module from the International Continence Society recommends the scan be done soon after voiding and prefers ultrasound to a catheter for this. It also makes an important point: there is no universally accepted definition of a significant residual. Your doctor reads the number with your symptoms, not against a single line.

What does the prostate volume on the report mean?

The ultrasound measures the gland in three directions and multiplies them by a formula to estimate volume. You’ll see it written as cc, ml or grams; for prostate tissue these come out roughly the same, which is why “prostate weight” and “prostate volume” appear on reports from different labs for the same thing.

Then there’s grading. Some reports add a grade (grade 1, 2, 3 enlargement). Grading systems aren’t standardised between centres, so a “grade 1” from one place isn’t directly comparable with another’s. Ask what volume the grade is based on.

Here’s the surprise. A big prostate doesn’t guarantee big trouble, and a modest one can cause plenty. The US National Institute of Diabetes and Digestive and Kidney Diseases notes that urinary symptoms may not be directly related to the size of the prostate. What matters is how the gland presses on the channel, and how the bladder muscle copes.

Is a raised PVR always a problem?

No. A single high reading has several innocent explanations, and most of them come down to how the test was done on that particular morning rather than to anything wrong with your bladder, so before you worry, check whether any of these fit your visit:

• Rushed or anxious voiding. Standing at an unfamiliar toilet with a queue outside, many men stop early.
• Delay. If the scan happens long after you’ve passed urine, the kidneys have already added more.
• Over full start. Holding a very full bladder for the first scan can overstretch the muscle so it doesn’t empty completely.

The teaching module also notes PVR is not a strong predictor of sudden retention and doesn’t by itself prove blockage. That’s why it is often repeated, sometimes on a different day and in calmer conditions, and why a urologist may add a flow test, a urine test, a kidney check or other assessment before deciding anything at all, rather than acting on one printed figure from one rushed visit.

How to prepare for a prostate ultrasound

1. Ask whether the scan is through the belly (transabdominal) or through the back passage (transrectal). Most first scans are through the belly.
2. For a belly scan, arrive with a comfortably full bladder: the centre will tell you how much water to drink beforehand and when to stop passing urine. Follow it exactly.
3. The first images are taken with the full bladder; then you’re sent to empty for the PVR.
4. Take your usual medicines unless told otherwise, and bring the list.
5. Bring your last PSA report if you have one, so the doctor can compare.

Your symptoms count more than the scan

Urologists often use a short symptom questionnaire, the International Prostate Symptom Score (IPSS). It asks how often you feel you haven’t emptied, how often you go within two hours, whether the stream stops and starts, urgency, weak stream, straining and night trips. Fill it in at home. Bring it.

Waking three times a night to pass urine is a quality of life problem whether the gland is 30 cc or 80 cc. The everyday causes of frequent urination, from chai in the evening to sugar, are covered in bar bar peshab aana, and the wider prostate symptom picture is in prostate badhna.

What happens after the report?

Mild symptoms? Often, nothing dramatic. For a man with mild symptoms, a small PVR and a moderately enlarged gland, the usual advice is about habits, such as less fluid late in the evening, fewer evening cups of chai and unhurried, double voiding, along with watchful waiting and a review at the interval the doctor sets. Larger residuals, repeated infections, blood in the urine, stones or kidney changes on the scan push the doctor towards closer follow up and further tests. Medicines and procedures are a specialist decision. Never start, stop or change one because of a scan number, and that includes over the counter products: tell the doctor if you take cold and cough medicines with decongestants or antihistamines, which can make passing urine harder. More reports are explained in Lab Reports Decoded.

Prostate ultrasound and PVR questions

Sources

• Asimakopoulos AD et al. Measurement of post-void residual urine (ICS teaching module). Neurourol Urodyn 2016
• NIDDK: Prostate enlargement (benign prostatic hyperplasia)