Approach
Diagnosis relies on recognising the different types of presentation. Acute presentations are often painful (e.g., urinary retention or urolithiasis). Chronic presentations may be more insidious and, if unilateral, the patient may have a normal creatinine and normal urine production. The diagnostic approach rests on recognising the possibility of obstruction within the urinary system, confirming this, and identifying the level of obstruction and ultimately the underlying cause.
Acute urinary retention
In a patient who presents in pain with a tense distended lower abdomen and a history of inability to pass urine for many hours, the diagnosis of retention is usually made clinically. In uncertain cases, a bladder ultrasound can assess bladder volume (>300 mL is indicative of retention; post-void residual volumes up to 300 mL may indicate incomplete emptying).
If retention is due to benign prostatic hyperplasia (BPH) or a urethral stricture, the patient is likely to have a history of worsening lower urinary tract symptoms. Age and past medical history give the clinician a reasonable idea of which is most likely. Older patients may have a history of lower urinary tract symptoms such as nocturia, urinary frequency, urgency, and weak or intermittent urinary stream, which are all suggestive of BPH. Younger patients with a history of pelvic trauma, STIs, or urethral instrumentation are more likely to have urethral stricture disease.
Diabetes mellitus or multiple sclerosis can cause retention due to nerve dysfunction of the bladder. The use of many medications, such as anticholinergic agents or opioid analgesics, may be a contributing factor.
Digital examination of the prostate may reveal the smooth enlargement of BPH, or a hard, nodular prostate with loss of the median sulcus, which is suspicious for malignancy. Difficulty in placing a catheter to relieve retention may occur due to BPH, meatal stenosis, or urethral stricture disease. If difficulty is encountered, consultation with a urologist is advised. In females, a careful bi-manual pelvic examination is performed to look for a cystocele, pelvic malignancy, or other anatomical abnormalities. If no causes are readily identified, a catheter should be placed and further evaluation undertaken by a urologist.
Systemic symptoms such as weight loss and physical findings such as lymphadenopathy may suggest underlying malignancy.
Investigations
Prostate specific antigen is not generally measured in the acute setting as levels are often falsely elevated. Levels usually return to baseline approximately 3 months after an acute event.
Renal colic
Patients with acute onset of unilateral flank pain should be evaluated for urolithiasis. The pain is usually severe and spasmodic in nature, and may be accompanied by flank tenderness. The patient may be nauseous and unable to lie still. This is usually accompanied by microscopic haematuria, which can be confirmed by a simple bedside urinary dipstick. Absence of microscopic haematuria does not exclude urolithiasis.
Investigations
If urolithiasis is suspected, a non-contrast computed tomography (CT) scan abdomen and pelvis is the imaging method of choice.[27] Non-contrast CT has 96% specificity and 97% sensitivity for urolithiasis.[28]
A CT scan abdomen and pelvis without and with contrast is recommended if the cause of pain is not identified by non-contrast CT, or if further distinction is needed (e.g., ureteral stone vs. phleboliths).[27]
Colour Doppler ultrasound kidneys, bladder, and retroperitoneum can be performed with an abdomen and pelvis x-ray (kidney, ureter, bladder [KUB]) as an alternative to CT.
Additional tests may be considered, but are generally thought to be less helpful than a CT or ultrasound with KUB. The intravenous pyelogram has excellent anatomic detail but is less sensitive than CT and is not recommended if the patient has renal insufficiency or is allergic to contrast. Magnetic resonance urography (MRU) without and with contrast can be considered.[27]
During pregnancy, ultrasound is the diagnostic procedure of choice for suspected urolithiasis.[27]
Infective symptoms
If a patient is febrile and has flank pain, it is important to exclude an obstructed and infected system. Urinary tract infection (UTI) in a patient with obstruction at any site in the urinary tract is a complicated UTI. Clinical presentation can vary and can include imminent urosepsis.[29]
Investigations
Basic metabolic profile, full blood count, and a midstream urine sample are useful to screen for infection.
Appropriate imaging with either ultrasound and/or non-contrast CT should be considered in patients with pyelonephritis who fail to improve within 24 to 48 hours, those with a history of urological disease, and those with symptoms of renal colic suggestive of urolithiasis.
In a patient with evidence of infection and urinary obstruction, sepsis should be clinically suspected in those with fever or hypothermia, leukocytosis or leukopenia, tachypnoea, and tachycardia. A validated scoring system, such as the quick Sequential [sepsis-related] Organ Failure Assessment (SOFA) score, can identify those at risk of deterioration. Patients with at least two of the following three criteria: respiratory rate of 22 breaths per min or greater, altered mental state (Glasgow Coma Scale score <15), or systolic blood pressure of 100 mmHg or less, are likely to have poor outcomes requiring escalation of therapy as appropriate.[29][30]
Urine culture and two blood cultures should be obtained, and imaging investigations performed early.[29] Parenteral high dose broad-spectrum antimicrobial therapy should be started within 1 hour of first clinical assumption of sepsis.[29]
Newborn with UTI
Assessment by a paediatric urologist is strongly recommended for newborns presenting with UTIs. Infections may be due to an obstructive cause such as a posterior urethral valve or a non-obstructive cause such as vesico-ureteric reflux. Acutely, catheter placement will relieve obstruction associated with posterior urethral valves.
Many infants are found to have hydronephrosis on routine antenatal ultrasound. The significance of this varies, but follow-up ultrasound imaging after birth is recommended.[31] If abnormalities persist, consultation with a paediatric urologist is recommended.
Investigations
Newborns with UTI should have a renal ultrasound initially to look for hydronephrosis.[32][33]
Following ultrasound, a voiding cystourethrogram may be performed to identify anatomical obstructive causes (e.g., posterior urethral valve) and differentiate these from non-obstructive vesico-ureteric reflux.
Chronic urinary symptoms
Patients may present with chronic renal insufficiency, recurrent UTIs, or overflow urinary incontinence.
Urological history may reveal symptoms such as frequency, urgency, weak stream, need to strain, difficulty maintaining stream, and incomplete emptying. Any history of previous urological procedures may also be important. Patients may have recently been using anticholinergic agents, opioid analgesics, or alpha receptor agonists. Many other medications can also cause urinary retention, so the patient's medication list (both prescription and over-the-counter) should be carefully checked.
Focused physical examination of the abdomen, external genitalia, vagina, and/or rectum can help guide management in patients with lower urinary tract symptoms.[34][35]
Investigations
A urinary dipstick is useful to assess for the presence of infection (chronic retention can predispose to infection due to urinary stasis).
Renal ultrasound is a useful investigation if there is evidence of renal insufficiency. It may demonstrate obstruction as the underlying cause. A post-micturition bladder ultrasound can measure the residual volume (>300 mL is diagnostic of retention).
Non-contrast CT is the preferred imaging modality when there is concern for urolithiasis, involving any part of the urinary tract.
Nuclear renography with a diuretic is useful in patients with hydronephrosis of unknown aetiology.[36] It can be used to assess kidney function and drainage.
Magnetic resonance urography without contrast may also be useful in pregnant women to look for stones or anatomic abnormalities.[27]
Weight loss, change in bowel habits, family history of malignancy
If there is suspicion of an underlying malignant process, further tests will be needed. These will depend on the type of malignancy suspected, but may include measurement of tumour markers such as prostate specific antigen and carcino-embryonic antigen, along with CT imaging of the abdomen and pelvis. Discussion with appropriate consultants is then advised.
Use of this content is subject to our disclaimer