Acute urinary retention and lower urinary tract obstruction

• Acute urinary retention is the sudden, often painful, inability to pass urine. It is an emergency: the bladder overfills, becomes painful and palpable, and the kidneys are put at risk if the obstruction continues.
• In men the usual cause is enlargement or obstruction of the prostate; in women the cause is more often pelvic organ prolapse, a urethral stricture, a stone, a neurological disorder or a drug. Many causes are reversible once found.
• The immediate treatment is catheterisation to empty the bladder safely, followed by treating the cause. An alpha blocker is started before the catheter is removed, to reduce the chance of recurrence.
• After the bladder is emptied, some people pass very large volumes of urine for a day or two. This is post-obstructive diuresis. It is managed by replacing only part of the urine output and repleting electrolytes, not by matching it litre for litre.
• A urethral stricture is a common, fixable cause of both retention and poor stream. It narrows the tube that carries urine out. For short strictures a single endoscopic division or dilatation is appropriate; longer or recurrent strictures need reconstruction.

By the end of this page you should be able to:

1. Define acute and chronic urinary retention and describe how bladder outlet obstruction produces them.
2. Take a focused history and examination that points to the likely cause, and choose the right initial tests.
3. Safely catheterise a patient with acute retention and explain the choice between urethral and suprapubic drainage.
4. Manage post-obstructive diuresis, including fluid replacement limits and electrolyte monitoring.
5. Recognise, investigate and manage urethral stricture, including when to refer for urethroplasty.
6. Adapt each step to a setting without specialist tests or surgical services.

Urinary retention is usefully split by time and by whether the problem is in the pipe or the pump.

• Acute retention begins over hours. The bladder is full and painful, the urge is strong and no urine comes. In older men it is the classic presentation that provokes a trip to the emergency department.
• Chronic retention begins slowly. The bladder fills to a large volume without pain, and the patient may be surprisingly unaware of it. Overflow dribbling, a poor stream, nocturia and constipation of urine lead eventually to an incidental or referral finding.
• Obstructive retention arises because something blocks the outlet: prostate enlargement, a stricture, a stone, a tumour or a clot.
• Non-obstructive (detrusor failure) retention arises because the bladder muscle cannot generate pressure: neuropathy, certain drugs (anticholinergics, alpha agonists), severe infection, or acute inflammation. The bladder is often large and soft but painless.

The symptom scales used to judge outlet obstruction also apply here. The International Prostate Symptom Score (IPSS) grades symptoms as mild (0 to 7), moderate (8 to 19) or severe (20 to 35), and it is a practical way to follow a man with lower urinary tract symptoms before retention occurs. ^[1]

Acute urinary retention occurs predominantly in older men, because prostate enlargement becomes common from the sixth decade. In women it is far less common and almost always signals a specific cause such as a urethral stricture, a large cystocele, a stone, a pelvic mass, infection, or a neurological condition. It also occurs in children, where posterior urethral valves and neuropathic bladders dominate.

Chronic retention is equally a disease of the same older male group, and a substantial minority of men present with an incidental large bladder residue found on examination or scan.

Urethral stricture is a major contributor. It is a narrowed segment of the anterior urethra caused by fibrosis and scarring of the urethral lining and the surrounding corpus spongiosum, called "spongiofibrosis". The incidence is estimated at 229 to 627 per 100,000 men, with a sharp rise after the age of 55 years and a mean age of presentation around 45 years. The anterior urethra is affected in about 92% of cases and the bulbar urethra in about 47%. ^[2]

Acute retention has three useful groupings: obstruction at the outlet, failure of the detrusor, and precipitating factors acting on a vulnerable bladder.

Bladder outlet obstruction

• Benign prostatic enlargement is the commonest cause in older men and is the main reason a man with mild symptoms is admitted for retention.
• Prostate cancer can present with obstruction; always consider it, particularly with a hard irregular prostate or a markedly raised prostate-specific antigen.
• Urethral stricture, described below.
• Bladder stone or a blood clot, both of which can jam the bladder neck.
• Urethral foreign body and urethral valves in children.

Non-obstructive (neurogenic or muscular)

• Peripheral neuropathy (diabetes, alcohol), spinal cord disease, multiple sclerosis, cauda equina and spinal trauma.
• Medications: anticholinergics, antimuscarinics, alpha agonists, decongestants, tricyclics, and excessive opioid analgesia.
• Severe cystitis, recent surgery or anaesthesia, faecal impaction and constipation.

Precipitants in a man who already has outflow narrowing

Sudden cold, alcohol, anticholinergic or decongestant medicines, a long wait with a full bladder, infection and surgical stress can tip a man with mild prostatic obstruction into retention.

Where glands are estimated to be over 30 g, or the PSA is over 1.4 ng/ml, 5-alpha reductase inhibitors are indicated for ongoing therapy, because they slowly shrink the gland and reduce progression. ^[1]

Urethral stricture: causes

Worldwide, the most common cause of a stricture is iatrogenic injury to the urethra from catheterisation or transurethral surgery. Infection of the urethra, especially gonorrhoea, used to account for about 40% of strictures in resource-rich countries, but now accounts for only about 1% to 5% there, while it remains a major cause, around 42% of strictures, in low-resource settings. ^[2] Trauma (straddle injury, pelvic fracture), lichen sclerosus (balanitis xerotica obliterans), hypospadias surgery, radiation and prostate surgery all produce strictures. Idiopathic strictures are common in the bulbar urethra.

Iatrogenic, catheter-related injury deserves particular attention, because prevention is the surest protection. About 11% to 16% of all urethral strictures follow catheterisation. In higher-quality studies, the pooled rate of urethral stricture or erosion after short-term catheterisation (less than three weeks) was about 3%. The risk rises to nearly 9% when the catheter stays in place for a prolonged period, as in spinal cord injury. About one in four hospital catheterisations are considered unnecessary. Training staff, choosing a catheter no larger than 18 French when drainage is the only aim, avoiding non-coated latex catheters, and refusing to allow a catheter when it is not needed all reduce this harm. ^[2]

The normal bladder is a low-pressure reservoir. At voiding the detrusor contracts against an outlet that is relaxed. Obstruction changes that.

When the outlet is narrowed, the detrusor must generate higher pressures to push urine through. Over months or years the muscle wall thickens and trabeculates. For a time this compensates, but the bladder becomes stiff and less compliant. Fibrosis follows. Once compensation fails, the bladder no longer empties, the residual volume rises and urine accumulates.

A strained bladder transmits pressure backwards: the ureters dilate and the kidneys swell. That is hydronephrosis, and it is the bridge between a local obstruction and renal failure, especially when the retention is chronic and painless, because the patient presents late.

In acute retention, pain is produced by sudden overstretching of the bladder wall and rising pressure. If overdistension continues, the detrusor can stretch enough to ischaemia, and bladder rupture is a rare but serious consequence.

The ability to hold a large volume without discomfort is a feature of chronic retention. The detrusor adapts by shifting its length-tension curve and by losing sensation, so the first complaints are leakage, nocturia and a poor stream rather than pain. This is why chronic retention is found late.

With a urethral stricture, the fibrotic ring narrows the lumen. The stream weakens, the bladder must work harder, and the same sequence of compensation and failure begins. Strictures below 10 French calibre usually cause a visible drop in flow. ^[2]

History in acute retention

• Sudden inability to pass urine, often preceded by a weak or hesitating stream, nocturia and urgency over months.
• Pain in the suprapubic region or lower abdomen that builds over hours. The patient can be agitated.
• Recent precipitants: a long car journey, alcohol, new anticholinergic or decongestant medication, cystitis, prostate surgery.
• In chronic retention: poor stream, straining, dribbling, nocturia and overflow wetting; often little or no pain.
• Screening questions for neurological disease, diabetes, pelvic surgery and trauma.

Examination

• A bladder that is full and tender in acute retention, rising above the pubic bone and sometimes to the umbilicus. In chronic retention the bladder is large but soft and non-tender.
• Inspect the external genitalia for a meatal stricture or scar.
• Rectal examination in men: prostate size, consistency, nodules and tenderness. A firm enlarged gland suggests benign enlargement; a hard irregular gland suggests malignancy.
• Neurological examination of the sacral nerves and sphincter tone.
• Abdomen, pelvis and lower limbs for thrombosis or oedema.
• In women, pelvic examination for cystocele or prolapse, both of which cause kinking and obstruction.

Timing and severity

A bladder that has become massively distended may take longer to recover its muscle function when drained, and the patient is at risk of an unstable contraction pattern for days or weeks.

Several conditions look like retention. The key is to separate a full bladder that cannot empty from a bladder that is empty but blocked at the distal urethra, and from a neurological pool with overflow.

The aim is to confirm retention, estimate how long the kidneys have been affected, and look for the cause.

Bedside

• Urinalysis (dipstick) for blood, glucose, protein, nitrites and leucocytes. A simple, cheap screen for infection and diabetes.
• Bladder scan, if available, to measure residual volume before and after any void.
• Post-void residual measurement by scan.
• Serum creatinine (with estimated glomerular filtration rate), particularly in chronic retention or when the kidneys are suspected to be affected.

First-line blood tests

• Full blood count, renal function, glucose.
• Prostate-specific antigen in men with larger glands or abnormal prostates, with counselling, because infection and instrumentation raise it.

Flow and pressure studies (specialist)

• Free uroflowmetry: a reduced peak flow for age and sex is abnormal in men.
• Post-void residual measurement by scan.
• Ultrasound of the kidneys and, in men with bothersome lower urinary tract symptoms, cystoscopy and upper tract imaging when clinically indicated.
• Multichannel cystometry if surgery is being considered, or if atypical features suggest detrusor overactivity or underactivity.

Imaging

• Ultrasound of the renal tracts for hydronephrosis, stones and bladder wall thickness.
• Computed tomography when a pelvic mass, cancer or complex stones are suspected.
• Voiding cystourethrogram (retrograde urethrogram) is the test of choice when a stricture is suspected: it shows the site, number and length of narrowings. ^[2]

There are no single numerical diagnostic criteria for acute retention beyond the clinical picture. Chronic retention is defined for practical purposes by retention of a post-void residue greater than 1 litre, or by a palpable or percussable bladder. In that situation, and when renal function or upper tracts are impaired, the retention is a surgical trigger. ^[1]

The International Prostate Symptom Score provides the baseline symptom score that guides whether active surveillance, drug treatment or surgery is appropriate, and it is repeated after any intervention. ^[1]

For stricture, diagnosis is radiological and endoscopic: a retrograde urethrogram with or without voiding cystourethrogram, supplemented by cystoscopy. RUG defines length and calibre, and cystoscopy determines whether the lumen is passable and whether the mucosa is healthy.

Men with acute retention must be catheterised immediately. The bladder should be allowed to drain completely. Pain falls as the pressure falls. ^[1]

• Give analgesia and position the patient appropriately.
• Use a urethral catheter if possible: a commonly chosen modest calibre, and no larger than 18 French when drainage is the only purpose. Lubricate generously.
• If the urethra will not accept a catheter, or if urethral trauma is suspected (blood at the meatus, pelvic fracture, perineal haematoma), use a suprapubic catheter inserted under ultrasound or open guidance.
• Do not use a catheter larger than 18 French when drainage is the only purpose; large catheters themselves cause urethral injury. ^[2]
• Use a modest balloon volume and avoid excessive traction.
• Check renal function and start fluid replacement as needed (see post-obstructive diuresis below).

If the patient is haemodynamically unstable, has sepsis, or has a tense painful abdomen, catheterisation combined with resuscitation and source control takes priority.

• An alpha blocker (for example, tamsulosin or alfuzosin) is offered before the catheter is removed; it starts to help within days and reduces the chance that the bladder will fail again. ^[1]
• In men with retention and an apparently large prostate, a 5-alpha reductase inhibitor is added for ongoing control. ^[1]
• For storage symptoms from overactive bladder after obstruction is relieved, anticholinergics or beta-3 adrenoceptor agonists can be used, but they may worsen retention if the outlet is still tight, so they are introduced cautiously.
• Distension cystitis is treated with hydration and analgesia.

• Transurethral resection, laser enucleation or incision of the prostate is the operation of choice for benign prostatic obstruction in men who fail medical therapy or have recurrent retention.
• Cystoscopy and bladder neck incision when the neck itself is the culprit.
• Removal of a stone or clot by litholapaxy or cystoscopy.
• Urethral stricture management, set out separately below.
• Referral for surgery where the anatomy is complex or the cause is unclear.

A trial without catheter is attempted once the precipitating cause has been treated, the patient is passing well, and the bladder has recovered. It is common to start an alpha blocker for several days first. If the patient voids successfully with low post-void residual, send him home and follow up. If he fails, re-catheterise and reconsider surgery; intermittent self-catheterisation is an alternative where surgery is unsuitable or declined.

• Serum creatinine testing and imaging of the upper urinary tract are recommended when chronic retention is suspected clinically (residual over 1 litre, or a bladder that is palpable or percussable) or when there is nocturnal enuresis, recurrent infection or a history of stones. ^[1]
• If renal function is impaired or the upper tracts are abnormal, drain the bladder with catheterisation before surgery. ^[1]
• If renal function is preserved and there are other bothersome voiding symptoms, surgery on the outlet without prior catheterisation may be considered. ^[1]
• Long-term catheterisation is offered when surgery is unsuitable and active surveillance is offered when the symptoms are non-bothersome and the tracts are normal. ^[1]
• Intermittent self-catheterisation is preferred, where possible, ahead of an indwelling catheter for chronic retention, and a suprapubic route is often better tolerated long-term.

Once a long-standing obstruction is relieved, the kidney is no longer held under pressure and it begins to clear the retained solutes and water. The result is a heavy diuresis. The expected physiological form lasts about a day; when it persists beyond 48 hours and drives electrolyte loss, hypotension or shock, it becomes pathological. ^[3]

Definitions used in practice: a urine output of at least 200 ml per hour for two consecutive hours, or more than 3 litres in 24 hours after relief of retention, is post-obstructive diuresis. ^[3]

The diagnostic and monitoring clues, and the reason they work, are these. ^[3]

• Urine sodium above 40 mmol/l and a urine osmolality below 450 mosmol/kg, or a specific gravity below 1.010, point to tubular dysfunction with impaired concentration (medullary washout), which is what makes the diuresis run on. ^[3]
• The mechanisms are medullary washout, down-regulation of sodium transport in the thick ascending limb, a fall in glomerular filtration during obstruction, and poor response to antidiuretic hormone, behaving like nephrogenic diabetes insipidus.
• The condition is triggered by obstruction from stones, enlargement of the prostate, faecal impaction, neurological bladder, or tumour.

Management follows from the mechanism:

• Document hourly urine output and measure electrolytes roughly every 12 hours.
• Replace only one half to two thirds of the hourly urine output with fluids, rather than matching it. Matching it drives more diuresis.
• Infuse crystalloid and replete potassium, magnesium, phosphate and calcium as measured, not by formula.
• Watch for hypotension and shock; pressors may be needed in the acute phase.
• Medicines that help restore the gradient and the concentrating ability, such as desmopressin and oral urea or a higher protein intake, have been used successfully in case reports when the diuresis is prolonged, but routine use is not established. ^[3]
• Continue until the urine output falls, the urine osmolality rises and renal function returns.

The teaching point is that the danger is not only too little fluid, but also too much: over-replacement keeps the washout going.

A stricture must be treated as a possible cause of any man with a weak stream, spraying, terminal dribbling, recurrent infection, or retention.

Investigation is radiological: a retrograde urethrogram, and voiding imaging where possible, to show site, number and length; cystoscopy to confirm whether the lumen is passable. Ultrasound of the urethra (sonourethrography) is a useful adjunct in specialist practice.

Options

• Observation for incidental high-calibre strictures above 16 French, which progress slowly. ^[2]
• Direct vision internal urethrotomy or single dilatation, first-line for a primary, single, short stricture under about 2 cm in the bulbar urethra. The five-year stricture-free rate can be as high as 77% in selected patients. ^[2]
• Visually controlled dilatation in preference to blind dilatation, with a low complication rate; blind repeated dilatation raises stricture complexity. ^[2]
• Intermittent self-dilatation, with intraurethral corticosteroid lubricant, to stabilise rather than cure a recurrent stricture when urethroplasty is not viable. ^[2]
• Drug-coated balloon dilatation, an option for a short bulbar stricture recurring after at least two prior endoscopic treatments in men who are not fit for or do not want urethroplasty. ^[2]
• Urethroplasty for longer, multiple, recurrent or penile strictures, and where endoscopic treatment has failed. Repeat endoscopic treatment delays better surgery. ^[2]

Rules that follow from the evidence and must not be broken: ^[2]

• Do not perform urethrotomy or dilatation for penile strictures. ^[2]
• Do not use endoscopic treatment alone for a stricture longer than 2 cm. ^[2]
• Do not repeat endoscopic treatment more than twice if urethroplasty is a realistic option. ^[2]
• Avoid urethral catheters larger than 18 French when drainage is the only purpose. ^[2]

Of urinary retention and obstruction itself:

• Acute kidney injury from back pressure, most dangerous in silent chronic retention.
• Hydronephrosis, stone formation and recurrent infection.
• Bladder ischaemia or, rarely, rupture with massive overdistension.
• Post-obstructive diuresis with electrolyte loss and shock, as above.
• Urethral injury from catheterisation (stricture, false passage, balloon inflation injury).
• Later instability of bladder function after drainage.

Of urethral stricture:

• Recurrence and progression to more complex disease if endoscopic treatment is repeated.
• Erectile dysfunction, particularly with penile stricture treatment and urethrotomy.
• Infection, strictures worsened by repeated instrumentation.
• Malignancy rarely at the stricture site in long-standing disease.

The outlook is determined by how long the bladder and kidneys have been obstructed. Acute retention treated promptly usually recovers organ function. In chronic retention the bladder may never return to normal contractility, even after surgery; the patient is left with a poorly contracting bladder and may need intermittent self-catheterisation. Renal function that has been lost to obstruction does not reliably return, which is why renal failure in silent chronic retention is the single most important avoidable complication.

Early referral and decompression change the prognosis more than any other intervention.

• Review all medicines for anticholinergic, alpha agonist or opioid burden in men with lower urinary tract symptoms.
• Treat constipation and faecal impaction, which both precipitate and worsen retention.
• Review diabetic control and other neuropathic risks.
• Reduce unnecessary catheterisation in hospital; train staff; use the smallest appropriate catheter; prefer intermittent catheterisation for chronic retention.
• Prostate screening is individualised and follows national guidelines; it is not recommended for all, and it does not prevent retention.
• Safe sexual practice and prompt treatment of urethritis prevent infective strictures. ^[2]

Older adults. Retention is both more common and more silent. Co-morbidities make catheterisation and surgery higher risk, and a suprapubic catheter may be the better long-term solution when surgery is unsuitable.

Children. Posterior urethral valves and other congenital anomalies dominate; a child with retention needs urology, not a catheter alone.

Women. Always look for prolapse, a stone, a urethral stricture or a pelvic mass. Retention is never "just prostate disease" in a woman. True female urethral strictures occur in 0.08% to 5.4% of women with refractory lower urinary tract symptoms, usually at the mid or distal urethra. ^[2]

Pregnancy. Retention late in pregnancy can result from impaction of the fetal head or fibroids; management is obstetric and urological together. A short course of alpha blocker is not appropriate in pregnancy; catheterisation is the treatment.

Immunocompromised and neuropathic patients. They hide symptoms and infection, so check post-void residual when the history is vague and infection is present.

Much of this topic can be done well with little technology:

• A plastic syringe and catheter, or a fine tube passed over a guidewire, will decompress almost every retention. When urethral passaging fails, a suprapubic catheter through a small incision is straightforward and safer than forcing a catheter.
• A hand-held bladder scan is not essential: the fullness of the bladder can be judged clinically and confirmed by passing a catheter.
• Renal function and ultrasound are valuable but, when absent, the clinical state of the kidneys (urine output, oedema, anaemia) guides decisions and referral.
• The fluid replacement rules for post-obstructive diuresis need only a urine jug, a measuring cup, a watch and clinical monitoring.
• Intermittent catheterisation kits are cheap and reusable when cleaned properly, and they allow patients to live at home between treatments.
• Urethral stricture prevention is mostly behaviour and training: avoiding unnecessary catheterisation and treating urethritis early cost little and avoid a lifetime of dilatations.
• For established strictures, internal urethrotomy and dilatation can be performed in basic operating rooms. Where they will not last, refer for urethroplasty rather than repeat dilatation.

• Acute urinary retention is sudden, painful and dangerous to the kidneys; treat it as an emergency and catheterise immediately.
• Obstruction is by far the commonest cause in men, usually benign prostatic enlargement; think also of cancer, stricture, stone and clot.
• In women, retention always needs an explanation found.
• Pain plus a palpable bladder defines acute retention; absence of pain with a large bladder defines chronic retention.
• An alpha blocker is started before the catheter is removed and lowers the relapse rate.
• Chronic retention with a post-void residue over 1 litre, or impaired kidney function or hydronephrosis, needs specialist planning and decompression before surgery.
• Post-obstructive diuresis is a feature of treatment, not just of disease; replace only one half to two thirds of the urine output, monitor electrolytes, and remember that over-replacement worsens it.
• Urethral stricture is a common, fixable cause of obstruction; iatrogenic injury and infection are its main causes.
• Endoscopic treatment suits only short single bulbar strictures under about 2 cm; longer, penile or recurrent strictures belong to urethroplasty.
• Never repeat dilatation or urethrotomy more than twice when urethroplasty is an option, and never use urethral catheters over 18 French when drainage is the only aim.
• Most of the early harm is avoidable: review medicines, manage constipation, and prevent unnecessary catheterisation.

Chronic kidney disease and hydronephrosis; benign prostatic hyperplasia and lower urinary tract symptoms in men; urinary incontinence; urinary tract infection; bladder stones; prostate cancer; cauda equina syndrome; acute kidney injury.