Urinary retention is the inability to voluntarily empty the bladder. The cause can be either mechanical (e.g., benign prostatic hyperplasia, tumors, urethral strictures) or functional (e.g., detrusor underactivity due to peripheral neuropathy, anticholinergic drugs). Patients with acute urinary retention (AUR) present with a sudden, painful inability to void and a tender, distended bladder on palpation. Patients with chronic urinary retention (CUR) are typically unable to void completely but do not experience pain. AUR is usually diagnosed clinically and is considered a urological emergency. Therefore, urgent bladder catheterization should precede diagnostics. Diagnostics include renal function tests to assess for renal damage (obstructive nephropathy) and ultrasound of the kidneys, ureter, and bladder to identify the underlying cause and possible complications (e.g., hydroureteronephrosis). Further evaluation depends on the patient history and physical examination. Treating the underlying cause (e.g., with alpha blockers and/or TURP for benign prostatic hyperplasia) is essential to prevent recurrence and complications of urinary retention (e.g., UTI, obstructive nephropathy).
Mechanical bladder outlet obstruction 
- Bladder neck obstruction
Enlarged prostate gland
- (most common)
- Acute (rare)
- Urethral narrowing
- Anterior vaginal wall prolapse (e.g., cystocele, urethrocele)
- Pelvic mass (e.g., malignancy, fibroids, endometriosis)
- Rectal mass
- Fecal impaction
Functional bladder outlet obstruction
Neurogenic lower urinary tract dysfunction (neurogenic bladder) 
Neurogenic lower urinary tract dysfunction is caused by disruption in the innervation of the and/or and is commonly classified by anatomical location.
- Suprasacral spinal cord lesion: spinal cord lesion at or above L1 → detrusor-sphincter dyssynergia with simultaneous contractions of the detrusor muscle and involuntary activation of the urethral sphincter → urinary retention and/or urge incontinence (spastic neurogenic bladder)
- Sacral or infrasacral lesions: peripheral nerve damage or spinal cord lesion below L1→ detrusor underactivity with normal or reduced urethral sphincter tone → urinary retention and overflow incontinence (flaccid neurogenic bladder)
- Suprapontine lesion: brain lesion above the pons → disruption in the inhibition of the pontine micturition center → involuntary detrusor contractions → urinary incontinence without urinary retention
Drug-induced urinary retention 
- Due to drugs that decrease detrusor activity, e.g.:
- Due to drugs that increase urethral sphincter tone, e.g.:
- Primary bladder neck obstruction: an idiopathic functional disorder characterized by failure of the bladder neck to open completely during micturition 
|Acute vs. chronic urinary retention|
|Acute urinary retention||Chronic urinary retention|
- Confirm acute urinary retention.
- Perform urgent .
- Obtain initial diagnostics for urinary retention (i.e., urinalysis, urine culture, BMP).
- Perform additional diagnostics as indicated.
- Initiate treatment of the underlying cause, e.g., . 
- Consider hospital admission for patients with significant comorbidities, neurological deficits, obstructive nephropathy, or UTI.
- Discharge otherwise healthy patients with an indwelling catheter and arrange an outpatient voiding trial 3–7 days later. 
- Refer patients to urology within 2–3 weeks if: 
- Voiding trial is unsuccessful
- AUR (e.g., hesitancy) were present prior to
Initial diagnostics 
- Bedside imaging: to confirm urinary retention
- Laboratory studies
Additional diagnostics 
Additional diagnostics should be obtained in consultation with urology to confirm the diagnosis, determine the, and rule out differential diagnoses.
- Laboratory studies, e.g.:
- Renal and bladder ultrasound to evaluate for hydroureteronephrosis, BPH, and bladder calculi
- Transrectal ultrasound to evaluate for prostate cancer
- Pelvic ultrasound and/or CT abdomen and pelvis to evaluate for extrinsic bladder neck compression
- MRI brain and/or spine to evaluate for neurological causes
- Cystoscopy with urine cytology for suspected bladder cancer
- See also “Imaging techniques in urology.”
- Urodynamic studies, e.g., uroflowmetry: to assess bladder function
Mechanical bladder outlet obstruction
- Enlarged prostate gland
- Urethral narrowing: Refer to urology for management (e.g., meatotomy for meatal stenosis, balloon dilation for urethral stricture).
- Other obstructive etiologies: : See “Treatment of urinary tract obstruction.”
Functional bladder outlet obstruction
Neurogenic bladder 
- Storage dysfunction
- Voiding dysfunction
- Further management may include:
- Minimally invasive interventions
- Surgical management 
- Drug-induced urinary retention: Discontinue or substitute the precipitating drug.
- Postoperative urinary retention: See “Postoperative urinary retention.”
- Primary bladder neck obstruction: Refer to urology for management (e.g., with alpha blockers, surgical incision of the bladder neck).
Complications of urinary retention
- Acute urinary retention: renal failure (acute kidney injury or obstructive nephropathy)
- Chronic urinary retention
Complications of bladder decompression 
Postobstructive diuresis 
- Definition: a polyuric state resulting from the rapid renal elimination of accumulated water and electrolytes after relief of urinary tract obstruction
- Etiology: typically occurs following relief of bladder outlet obstruction or bilateral ureteral obstruction
- > 200 mL/hour urine produced for 2 hours
- OR > 3 L urine produced in 24 hours
- Complications: dehydration, electrolyte imbalance, hypovolemia
Other complications of decompression
We list the most important complications. The selection is not exhaustive.