Post-void residual volume (PVR) is the amount of urine retained in the bladder after a voluntary void and functions as a diagnostic tool. A post-void residual volume helps in the evaluation of many disease processes, including but not limited to neurogenic bladder, cauda equina syndrome, urinary outlet obstruction, mechanical obstruction, medication-induced urinary retention, postoperative urinary retention, and urinary tract infections. Evaluating for post-void residual is typically performed using ultrasound, a bladder scanner, or with a urinary catheter.
A urine specimen is not always indicated but can aid in the diagnostic evaluation, especially if there is a concern for infection as the etiology of the elevated residual volume. Urinary catheterization after voiding can provide both a post-void residual and a urine specimen. Urinary catheterization should be performed sterilely to prevent infection and to obtain an uncontaminated urine specimen. See below for urinary catheterization technique.
Post-void residual evaluation is by measuring the remaining urine in the bladder shortly after a voluntary void; this can be accomplished through ultrasound, bladder scan, or by directly measuring the urine volume drained by a urinary catheter. Urinary catheterization is the gold standard for measuring the post-void residual.
Measurement of post-void residual immediately after voiding is crucial for accurate measurement, with delays of as little as 10 minutes from bladder emptying to post-void residual measurement potentially causing clinically significant overestimation of post-void residual.
Ultrasound (conventional or real-time ultrasound)
The conventional ultrasound is used to visualize the bladder directly, either transabdominally or transvaginally. It measures the bladder’s volume using the ultrasound machine's internal volume calculations or the mathematical equation seen below. Transvaginal ultrasound appears especially accurate for measuring low bladder volumes.
Most ultrasound machines have a function to automatically calculate volumes from the measurements used with the ultrasound calipers. If this function is not available the volumes can also be calculated using the prolate ellipsoid formula. Though there are multiple mathematical methods to calculate volume, the prolate ellipsoid is one accepted method, and the formula follows:
The bladder is measured at its maximal transverse (width), longitudinal (length) and anterior-posterior (height) diameters. This method is recommended as the standard calculation because it is fast and easy.
Data on the accuracy of transabdominal ultrasound for determining post-void residual is mixed. Although most studies demonstrate high accuracy of post-void residual using transabdominal point-of-care ultrasound or bladder scanners with automated measurement of bladder volume, other recent studies have brought their accuracy into question.
The portable bladder ultrasound device (commonly known as a bladder scanner)
A portable bladder ultrasound device uses ultrasound to specifically measure the three-dimensional volume of urine in the bladder. It is a non-invasive approach to identifying post-void residual.
The patient lies supine, ultrasound gel is to be placed at the suprapubic area, and the probe is then placed on the gel and directed toward the patient's bladder. The button is depressed, initiating the machine's evaluation of the bladder's volume, which is then displayed for the operator to see. The process can be repeated to better align the bladder in the center of the display. The largest volume is recorded. Different bladder scanner machines may have slightly different procedures, but the basics of the technique are similar across devices.
Bladder scanning is not suitable for use on patients with severe abdominal scars, prolapses of the uterus, or current pregnancy.  Abdominal ascites appears to cause falsely elevated measurements in some cases. There is some evidence that bladder scanners are more accurate than two-dimensional ultrasound imaging.
Urethral catheterization directly measures the post-void residual and is considered the gold standard for determining post-void residual, although there may be variable volumes present after catheterization, depending on the size and type of catheter used for drainage.
The male and female anatomy requires different techniques with inserting a urethral catheter, but the overall procedure and sterile technique are similar. Perform hand hygiene and place the patient in position of accessibility; a female patient should be placed in the frog-leg position, sterile drapes should cover the genitals with the urethral meatus exposed. Don sterile gloves. The non-dominant hand should hold the penis at a 90-degree angle toward the ceiling, and for females, the labia should be separated and held to expose the urethral meatus. The urethral meatus and glans penis for males or perineum for females should undergo prepping with an antiseptic solution using sterile technique. Insert a well-lubricated catheter into the urethral meatus with the dominant, sterile-gloved hand, and observe for a spontaneous return of urine to confirm placement in the bladder. Once placement is confirmed, inflate the catheter balloon with sterile water or saline. For in-out catheterization to obtain a post-void residual, allowing the bladder to drain completely into a graduated container and measure the volume, then remove the catheter; this should be performed shortly after a voluntary void to ensure an accurate post-void residual.
Comparison of bladder scanner to urinary catheterization:
A post-void residual measurement is a diagnostic tool used when there is a concern for underlying neurological disease/injury, bladder dysfunction, mechanical obstruction, infection or medication-induced urinary retention.
Symptoms of urinary retention and post-void residual can be indirect. A common presenting symptom of acute urinary retention is low abdominal pain and inability to pass urine, although, in young children or patients with dementia, who provide limited history, agitation may be the only sign of bladder distension.
Patients with cauda equina syndrome may present with low back pain, saddle anesthesia, bilateral sciatica, motor weakness of the lower extremities, paraplegia, or incontinence.
Young children may have urinary retention due to refusing to urinate because of the pain of urination caused by a UTI.
Underlying causes of elevated post-void residual include (but not limited to):
Infectious and/or inflammatory
For both sexes, there is a lack of consensus about what constitutes a significantly elevated post-void residual volume, and there is conflicting data. See below for general normal post void residual values.
Urinary catheterization is the gold standard to measure post-void residual volume but has some limitations such as discomfort, low compliance, and risk of urinary tract infection or injury. One study of post-op females found the overall prevalence of UTI after catheterization was 2.3%, but the risk of UTI rose the longer the catheter was in place.
In cases of urinary obstruction relieved by catheterization, post-obstructive diuresis (typically in cases of over 1500 mL of retained urine) can cause hypovolemia and electrolyte abnormalities that may require admission for management.
A post-void residual is a diagnostic tool to evaluate for underlying pathology.
Bladder scanning and real-time transabdominal ultrasound is non-invasive and has no risk of ionizing radiation. Urethral catheterization carries some risks including, hematuria, urethral injury, discomfort, and infection.
Although there is no consensus of what defines an elevated post-void residual volume, the post-void residual, in addition to history and physical exam, can help identify and diagnose urinary retention, and therefore determine the proper management, and prevent further disability or death.
|||Kim TH,Kim HS,Park JW,Lim OK,Park KD,Lee JK, Falsely Elevated Postvoid Residual Urine Volume in Uterine Myoma. Annals of rehabilitation medicine. 2017 Apr; [PubMed PMID: 28503470]|
|||Haylen BT,Lee J, The accuracy of post-void residual measurement in women. International urogynecology journal and pelvic floor dysfunction. 2008 May; [PubMed PMID: 18301853]|
|||Haylen BT, Verification of the accuracy and range of transvaginal ultrasound in measuring bladder volumes in women. British journal of urology. 1989 Oct; [PubMed PMID: 2684334]|
|||Byun SS,Kim HH,Lee E,Paick JS,Kamg W,Oh SJ, Accuracy of bladder volume determinations by ultrasonography: are they accurate over entire bladder volume range? Urology. 2003 Oct; [PubMed PMID: 14550437]|
|||Rachaneni S,McCooty S,Middleton LJ,Parker VL,Daniels JP,Coomarasamy A,Verghese TS,Balogun M,Goranitis I,Barton P,Roberts TE,Deeks JJ,Latthe P, Bladder ultrasonography for diagnosing detrusor overactivity: test accuracy study and economic evaluation. Health technology assessment (Winchester, England). 2016 Jan; [PubMed PMID: 26806032]|
|||Dicuio M,Pomara G,Menchini Fabris F,Ales V,Dahlstrand C,Morelli G, Measurements of urinary bladder volume: comparison of five ultrasound calculation methods in volunteers. Archivio italiano di urologia, andrologia : organo ufficiale [di] Societa italiana di ecografia urologica e nefrologica. 2005 Mar; [PubMed PMID: 15906795]|
|||Hvarness H,Skjoldbye B,Jakobsen H, Urinary bladder volume measurements: comparison of three ultrasound calculation methods. Scandinavian journal of urology and nephrology. 2002; [PubMed PMID: 12201931]|
|||Bent AE,Nahhas DE,McLennan MT, Portable ultrasound determination of urinary residual volume. International urogynecology journal and pelvic floor dysfunction. 1997; [PubMed PMID: 9449296]|
|||Ouslander JG,Simmons S,Tuico E,Nigam JG,Fingold S,Bates-Jensen B,Schnelle JF, Use of a portable ultrasound device to measure post-void residual volume among incontinent nursing home residents. Journal of the American Geriatrics Society. 1994 Nov; [PubMed PMID: 7963206]|
|||Park YH,Ku JH,Oh SJ, Accuracy of post-void residual urine volume measurement using a portable ultrasound bladder scanner with real-time pre-scan imaging. Neurourology and urodynamics. 2011 Mar; [PubMed PMID: 20658544]|
|||Mainprize TC,Drutz HP, Accuracy of total bladder volume and residual urine measurements: comparison between real-time ultrasonography and catheterization. American journal of obstetrics and gynecology. 1989 Apr; [PubMed PMID: 2653036]|
|||Alnaif B,Drutz HP, The accuracy of portable abdominal ultrasound equipment in measuring postvoid residual volume. International urogynecology journal and pelvic floor dysfunction. 1999; [PubMed PMID: 10450819]|
|||Teng CH,Huang YH,Kuo BJ,Bih LI, Application of portable ultrasound scanners in the measurement of post-void residual urine. The journal of nursing research : JNR. 2005 Sep; [PubMed PMID: 16237633]|
|||Haylen BT,Frazer MI,MacDonald JH, Assessing the effectiveness of different urinary catheters in emptying the bladder: an application of transvaginal ultrasound. British journal of urology. 1989 Oct; [PubMed PMID: 2684335]|
|||Clayton JL, Indwelling Urinary Catheters: A Pathway to Health Care-Associated Infections. AORN journal. 2017 May; [PubMed PMID: 28454610]|
|||Bhatt NR,Davis NF,Addie D,Flynn R,McDermott TED,Manecksha RP,Thornhill JA, Evaluating the cost of iatrogenic urethral catheterisation injuries. Irish journal of medical science. 2017 Nov; [PubMed PMID: 27052967]|
|||Chenoweth C,Saint S, Preventing catheter-associated urinary tract infections in the intensive care unit. Critical care clinics. 2013 Jan; [PubMed PMID: 23182525]|
|||Kelly CE, Evaluation of voiding dysfunction and measurement of bladder volume. Reviews in urology. 2004; [PubMed PMID: 16985853]|
|||Thomas K,Chow K,Kirby RS, Acute urinary retention: a review of the aetiology and management. Prostate cancer and prostatic diseases. 2004; [PubMed PMID: 14999235]|
|||Orendácová J,Cízková D,Kafka J,Lukácová N,Marsala M,Sulla I,Marsala J,Katsube N, Cauda equina syndrome. Progress in neurobiology. 2001 Aug; [PubMed PMID: 11311464]|
|||Kaplan SA,Wein AJ,Staskin DR,Roehrborn CG,Steers WD, Urinary retention and post-void residual urine in men: separating truth from tradition. The Journal of urology. 2008 Jul; [PubMed PMID: 18485378]|
|||Asimakopoulos AD,De Nunzio C,Kocjancic E,Tubaro A,Rosier PF,Finazzi-Agrò E, Measurement of post-void residual urine. Neurourology and urodynamics. 2016 Jan; [PubMed PMID: 25251215]|
|||Sakakibara R,Yamamoto T,Uchiyama T,Liu Z,Ito T,Yamazaki M,Awa Y,Yamanishi T,Hattori T, Is lumbar spondylosis a cause of urinary retention in elderly women? Journal of neurology. 2005 Aug; [PubMed PMID: 15778810]|
|||Chung KL,Chao NS,Liu CS,Tang PM,Liu KK,Leung MW, Abnormal voiding parameters in children with severe idiopathic constipation. Pediatric surgery international. 2014 Jul; [PubMed PMID: 24828888]|
|||Chang SJ,Yang SS, Variability, related factors and normal reference value of post-void residual urine in healthy kindergarteners. The Journal of urology. 2009 Oct; [PubMed PMID: 19695621]|
|||Chang SJ,Chiang IN,Hsieh CH,Lin CD,Yang SS, Age- and gender-specific nomograms for single and dual post-void residual urine in healthy children. Neurourology and urodynamics. 2013 Sep; [PubMed PMID: 23595887]|
|||Alagiakrishnan K,Valpreda M, Ultrasound bladder scanner presents falsely elevated postvoid residual volumes. Canadian family physician Medecin de famille canadien. 2009 Feb; [PubMed PMID: 19221075]|
|||Kolman C,Girman CJ,Jacobsen SJ,Lieber MM, Distribution of post-void residual urine volume in randomly selected men. The Journal of urology. 1999 Jan; [PubMed PMID: 10037383]|
|||Shimoni Z,Fruger E,Froom P, Measurement of post-void residual bladder volumes in hospitalized older adults. The American journal of medicine. 2015 Jan; [PubMed PMID: 25193275]|
|||Domen PM,Hofman PA,van Santbrink H,Weber WE, Predictive value of clinical characteristics in patients with suspected cauda equina syndrome. European journal of neurology. 2009 Mar; [PubMed PMID: 19490073]|
|||Prentice DM,Sona C,Wessman BT,Ablordeppey EA,Isakow W,Arroyo C,Schallom M, Discrepancies in measuring bladder volumes with bedside ultrasound and bladder scanning in the intensive care unit: A pilot study. Journal of the Intensive Care Society. 2018 May; [PubMed PMID: 29796068]|
|||Karp NE,Kobernik EK,Kamdar NS,Fore AM,Morgan DM, Length of Catheter Use After Hysterectomy as a Risk Factor for Urinary Tract Infection. Female pelvic medicine [PubMed PMID: 28914703]|
|||Leslie SW,Sharma S, Postobstructive Diuresis 2019 Jan; [PubMed PMID: 29083564]|
|||Todd NV, Guidelines for cauda equina syndrome. Red flags and white flags. Systematic review and implications for triage. British journal of neurosurgery. 2017 Jun; [PubMed PMID: 28637110]|
|||Nseyo U,Santiago-Lastra Y, Long-Term Complications of the Neurogenic Bladder. The Urologic clinics of North America. 2017 Aug; [PubMed PMID: 28716317]|
|||Kim BR,Lim JH,Lee SA,Kim JH,Koh SE,Lee IS,Jung H,Lee J, The Relation between Postvoid Residual and Occurrence of Urinary Tract Infection after Stroke in Rehabilitation Unit. Annals of rehabilitation medicine. 2012 Apr; [PubMed PMID: 22639750]|
|||Tseng TY,Stoller ML, Obstructive uropathy. Clinics in geriatric medicine. 2009 Aug; [PubMed PMID: 19765491]|
|||Mirone V,Imbimbo C,Longo N,Fusco F, The detrusor muscle: an innocent victim of bladder outlet obstruction. European urology. 2007 Jan; [PubMed PMID: 16979287]|