Urinary Retention is the inability to empty the urinary bladder adequately, either suddenly or gradually. Acute urinary retention is typically characterised by a rapid inability to pass urine accompanied by a painful, distended bladder and requires urgent assessment, whereas chronic urinary retention may develop more gradually and can sometimes produce surprisingly few symptoms despite substantial residual urine.
Retention is different from reduced urine production: a person with retention may continue producing urine normally but be unable to expel it from the bladder. It is also different from urinary incontinence, although chronic retention can cause overflow leakage when bladder pressure exceeds outlet resistance. Causes can involve obstruction at or below the bladder outlet, impaired detrusor contraction, neurological dysfunction, medications, inflammation, postoperative effects, or combinations of these mechanisms.
Bladder emptying requires coordinated contraction of the detrusor muscle with relaxation of the bladder outlet and urethral sphincter. Mechanical obstruction can prevent urine from passing even when the detrusor contracts effectively. In men, benign enlargement of the prostate is a common cause of bladder outlet obstruction, while urethral stricture, stones, pelvic masses, prolapse, or postoperative anatomical changes can also obstruct flow. Functional obstruction can arise when the sphincter fails to relax appropriately.
Detrusor underactivity can result from neurological disease, chronic overdistension, diabetes-related neuropathy, spinal disorders, or other causes. Some medicines can impair bladder contraction or increase outlet resistance. The distinction between obstruction and impaired contractility is important because relieving an obstruction does not necessarily restore normal detrusor function when the bladder muscle has been chronically damaged.
Acute urinary retention may cause severe lower abdominal or suprapubic pain, an intense urge to urinate, inability to void, and a palpable or distended bladder. Chronic retention may instead produce weak stream, hesitancy, intermittency, prolonged voiding, incomplete emptying, urinary frequency, nocturia, recurrent infections, or overflow leakage. Some patients have relatively few symptoms despite substantial residual urine, particularly when retention develops slowly. Severe retention can increase pressure within the urinary tract and may cause hydronephrosis and impairment of kidney function. Fever or systemic illness in a person with retention raises concern for associated infection. Neurological symptoms such as new leg weakness, saddle sensory disturbance, or loss of bowel control can indicate a potentially urgent neurological cause requiring immediate evaluation.
Diagnosis involves establishing that significant urine remains in the bladder after attempted voiding and identifying why. Bladder scanning with ultrasound can rapidly estimate post-void residual volume and is commonly used in clinical practice. Catheterisation provides direct drainage and can also provide an accurate measurement of retained urine. Urinalysis and culture may identify infection, while blood tests can assess kidney function and metabolic consequences. Physical examination may assess the abdomen, genital region, prostate where appropriate, pelvic structures, and neurological function.
Further testing can include uroflowmetry, formal urodynamic studies, cystoscopy, or imaging when the cause is uncertain or structural disease is suspected. The numerical definition of chronic retention is not based on a single universally applicable residual volume, because clinical significance depends on symptoms, duration, kidney function, infection risk, and the underlying cause.
Acute retention is commonly treated initially by prompt bladder decompression, usually with a urinary catheter, while the underlying cause is investigated and addressed. Catheterisation relieves pressure and pain but does not itself correct the disorder that caused retention. Depending on the cause, subsequent management may include medicines that reduce outlet resistance, treatment of infection or inflammation, removal of an obstructing lesion, urethral procedures, or surgery.
In men with prostate-related obstruction, alpha-adrenergic blockers may facilitate subsequent attempts to void in appropriate circumstances, while longer-term prostate-directed therapy may be considered depending on the clinical situation. Intermittent self-catheterisation can be an important long-term strategy for individuals with chronic incomplete emptying caused by neurogenic or detrusor disorders.
Chronic retention can produce significant complications because persistently elevated bladder pressure and residual urine can interfere with normal urinary tract function. Recurrent urinary infections can occur because residual urine provides a reservoir in which organisms can persist. High bladder pressure can transmit pressure towards the upper urinary tract and contribute to hydronephrosis and renal impairment. Bladder muscle changes can include hypertrophy, altered compliance, diverticulum formation, or eventual decompensation.
Overflow incontinence may occur when an overfilled bladder leaks intermittently, which can be mistaken for a primary continence disorder. Acute retention can also occur after surgery, anaesthesia, childbirth, medication changes, or abrupt worsening of chronic obstruction. Prompt recognition is therefore important even when symptoms are not dramatic.
Management of chronic retention requires attention to the underlying mechanism and to the practical burden of bladder drainage. Intermittent catheterisation can reduce complications and preserve bladder function in selected patients, while long-term indwelling catheters carry risks including infection, trauma, blockage, and discomfort. Surgical correction may be necessary when mechanical obstruction cannot be adequately managed with medication. Neurological evaluation can be important when retention results from spinal or peripheral nerve dysfunction.
Monitoring kidney function and upper-tract imaging may be appropriate when retention is substantial or associated with high bladder pressures. Treatment decisions should account for bladder function, residual volume, renal status, infection history, anatomy, dexterity, cognition, and patient preferences rather than focusing solely on whether a person can pass some urine.
A common misconception is that urinary retention means complete absence of urination. Chronic retention can coexist with frequent small-volume voiding and leakage, and some patients may continue to pass urine despite retaining a large residual volume. Another misconception is that all retention is caused by prostate enlargement; women, younger people, children, and people with neurological disorders can also develop retention through different mechanisms.
Retention should also not be confused with anuria or oliguria, which concern reduced urine production rather than failure to empty the bladder. Sudden inability to urinate, especially with severe pain or neurological symptoms, is clinically urgent. Recognising retention early can prevent bladder overdistension, infection, upper-tract damage, and potentially irreversible impairment of bladder or kidney function.
