Calculate and interpret post-void residual urine volume, voiding efficiency, and flow rate. Assess urinary retention severity and guide clinical evaluation.
Post-void residual (PVR) volume is the amount of urine remaining in the bladder after a voluntary void. It is a critical measurement in urology, gynecology, and primary care for evaluating urinary retention, bladder outlet obstruction, and neurogenic bladder dysfunction. Normal PVR is typically less than 50 mL; values above 200 mL are clinically significant.
This calculator computes PVR from pre-void bladder volume and voided volume, or accepts a directly measured PVR from catheterization or bladder ultrasound. It also calculates voiding efficiency (the percentage of bladder contents successfully expelled) and estimated flow rate, which together paint a comprehensive picture of lower urinary tract function.
Measurement of PVR is recommended for patients with urinary frequency, hesitancy, weak stream, incomplete emptying sensation, recurrent UTIs, and before starting medications that affect bladder function. Both bladder scan (non-invasive ultrasound) and catheterization methods are supported by this calculator. Check the example with realistic values before reporting.
PVR measurement is a fundamental diagnostic tool in urology that helps differentiate between overactive bladder (frequent voids with low PVR) and urinary retention (infrequent voids with high PVR). This distinction is critical because the treatments are opposite — anticholinergics for overactive bladder can worsen retention, while alpha-blockers for retention may worsen urgency. Accurate PVR assessment prevents misdiagnosis and inappropriate treatment.
PVR = Pre-Void Volume − Voided Volume (or direct measurement) Voiding Efficiency = (Voided Volume / Pre-Void Volume) × 100% Flow Rate = Voided Volume / Voiding Time (mL/s)
Result: PVR = 150 mL (Moderately Elevated), Voiding Efficiency = 62.5%, Flow Rate = 8.3 mL/s
With 400 mL pre-void volume and 250 mL voided, PVR is 150 mL (moderately elevated). Voiding efficiency is 62.5% (below the 80% ideal). Flow rate of 8.3 mL/s suggests reduced flow. Further evaluation with urodynamics may be warranted.
Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.
Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use. ## Practical Notes
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PVR less than 50 mL is considered normal. Values of 50–100 mL are mildly elevated and may not require intervention. Above 100 mL should prompt further evaluation, and above 200 mL typically requires treatment.
Catheterization is the gold standard but invasive. Bladder ultrasound scan has accuracy within ±15–25% of actual volume and is preferred for routine screening due to its non-invasive nature and lower infection risk.
PVR should be checked when symptoms of retention are present, before starting anticholinergic medications, during monitoring of BPH treatment, and in patients with neurogenic bladder. Serial measurements are useful for tracking treatment response.
Anticholinergics (used for overactive bladder), opioids, antihistamines, decongestants (pseudoephedrine), tricyclic antidepressants, and antipsychotics can all impair bladder contractility and increase PVR. Use this as a practical reminder before finalizing the result.
Acute urinary retention (complete inability to void) requires immediate catheterization. Chronic retention with PVR > 300 mL, recurrent UTIs due to retention, or upper tract damage (hydronephrosis) may require intermittent or indwelling catheterization.
Yes. Chronic significant urinary retention can cause vesicoureteral reflux (backflow to kidneys), leading to hydronephrosis and potentially kidney damage. This is why persistent elevated PVR requires monitoring and treatment.