Post-Void Residual of 150 mL: Is It Normal, and What Happens Next?

A post-void residual of 150 mL is not normal, but it is not an emergency either. It means about 150 mL of urine, roughly two-thirds of a cup, was still in your bladder after you had emptied it as well as you could. Most men leave far less behind. It is also only half of 300 mL, the level an American Urological Association expert panel uses to define chronic urinary retention, and it is a single reading of a measurement that is known to jump around.

So the honest answer is: higher than it should be, worth a repeat measurement, and worth understanding. Not a reason on its own for a catheter or surgery.

What most men leave behind

The best picture of normal comes from a Mayo Clinic study that scanned 477 randomly selected men from the community in Olmsted County, Minnesota, right after they urinated. The median residual was 9.5 mL. Half the men had between 2.5 and 35 mL. A residual of 150 mL is therefore several times what a typical man leaves.

Two findings from the same study are worth knowing. The residual was not linked to age, to how bad the men's urinary symptoms were, or to their flow rate. It was linked to prostate size: men with a prostate over 30 mL had 2.5 times the odds of a residual above 50 mL. And men with a residual above 50 mL, or an enlarged prostate, were about three times as likely to need a catheter for acute urinary retention over the next three to four years.

Why one scan settles nothing

Residual urine is one of the least repeatable measurements in urology. In a British study, 40 men waiting for prostate surgery had their residual measured by ultrasound six times over three months. One third had fairly stable readings. The other two-thirds varied by 150 to 670 mL between visits. The authors concluded that a residual cannot be determined reliably from a single measurement.

The variation was smaller in men whose average residual was under 100 mL, and larger the higher the average. A one-off 150 mL is therefore exactly the kind of reading that needs repeating. The European Association of Urology's 2026 guideline gives the same reason for why no residual volume has yet been agreed as a threshold for treatment: test-retest variability is large and outcome studies are lacking.

If you are rescanned, it helps to empty your bladder normally, in private and without rushing, and to be scanned soon afterwards. A bladder scanned some time after voiding has already started to refill.

What 150 mL does and does not tell you

It does not prove a blockage. A high residual can come from a prostate that obstructs the outflow, or from a bladder muscle that does not squeeze hard enough, which is called detrusor underactivity. The EAU guideline reports that at a 50 mL threshold, residual volume predicts obstruction correctly only about 63 percent of the time when it is high, and 52 percent of the time when it is low. Telling the two apart takes a pressure-flow study, and the answer matters for which treatment is likely to help.

It is not a reason to stop watchful waiting or medication. The EAU guideline says a large residual is not a contraindication to either, though it may predict a poorer response, especially to watchful waiting.

It is a reason to keep measuring. The guideline notes that following the residual over time may identify men at risk of acute retention, the sudden inability to pass urine that needs a catheter.

Where 150 mL matters most: bladder-relaxing drugs

The one place where 150 mL is a working line is overactive bladder medication. Antimuscarinics such as tolterodine, solifenacin and fesoterodine relax the bladder muscle, which can raise the residual. The EAU guideline states that acute retention is rare in men with a residual under 150 mL before treatment, both on these drugs alone and combined with an alpha blocker such as tamsulosin. The trials behind those drugs only included men with low residuals. The guideline then draws the line explicitly: do not use these medications, alone or added to an alpha blocker, in men with a residual above 150 mL. Both recommendations are rated weak, meaning they rest on limited evidence, but they are clear.

So 150 mL sits exactly on that line. If one of these drugs is suggested for urgency or frequency, a repeat scan first is the sensible step, because a second reading above 150 mL puts you in the group the guideline advises against treating with them. If you do start one, the guideline advises regular rechecks of the residual and stopping if your stream or emptying gets worse.

Alpha blockers such as tamsulosin and alfuzosin work the other way, relaxing the prostate and bladder neck to make emptying easier. They are not the concern here.

When a residual becomes chronic retention

The AUA expert panel defines non-neurogenic chronic urinary retention as a residual over 300 mL, found on at least two occasions and lasting at least six months. It is classed as high risk when there is hydronephrosis, meaning urine backing up and stretching the kidneys, stage 3 kidney disease, or repeated proven urinary tract infections.

At 150 mL you are well under that line. The EAU's assessment algorithm does treat a significant residual as a reason to scan the kidneys and, where needed, check kidney function, which is a simple way to make sure the residual is not doing harm.

A fairer number: how much of your bladder you empty

Because the residual depends on how full the bladder was to start with, the EAU guideline describes bladder voiding efficiency as an alternative: the volume you passed divided by the total, times 100. If you passed 300 mL and left 150 mL, you emptied 67 percent. If you passed 450 mL and left 150 mL, you emptied 75 percent. The guideline says this measure seems more reliable than the residual alone, especially in men with a weak bladder.

If your scan was taken after you passed only a small amount, ask how much you voided. The same 150 mL means something different after a 100 mL void than after a 400 mL one.

What to ask your doctor

Can we repeat the scan, ideally after a normal, unhurried void? How much did I pass before the scan? Is the cause more likely my prostate or my bladder muscle, and would a flow test or pressure-flow study tell us? Should my kidneys be scanned? And if a bladder-relaxing medicine is on the table, when will my residual be rechecked?

Get help the same day if you cannot pass urine at all, if your lower belly is painful and swollen, or if you have a fever with urinary symptoms. Those are signs of acute retention or infection, not of a borderline number.