5.4 Urology: Urinary Tract Infections, Renal Colic & Urinary Retention

Urology: Urinary Tract Infections, Renal Colic & Urinary Retention

Urological pathology spans a broad spectrum of acute clinical encounters in the United Kingdom, from community-acquired uncomplicated cystitis to time-critical emergencies such as septic obstructed nephropathy and acute urinary retention. Rapid differentiation of uncomplicated conditions from obstructive or systemic emergencies is vital to prevent permanent parenchymal loss and fatal sepsis.

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1. Urinary Tract Infections: Lower UTI vs. Acute Pyelonephritis

Urinary tract infections (UTIs) are primarily caused by ascending colonic gram-negative uropathogens. Escherichia coli accounts for 75–80% of all community-acquired infections. Other causative organisms include Staphylococcus saprophyticus (frequently isolated in young, sexually active females), Klebsiella pneumoniae, Enterococcus faecalis, and Proteus mirabilis (a urease-producing organism that hydrolyses urea to ammonia, producing an alkaline urine pH > 7.0 that precipitates magnesium ammonium phosphate struvite staghorn calculi).

Clinical Presentation & Diagnostic Differentiation

• Lower UTI (Acute Cystitis): Localised inflammation of the bladder mucosa. Clinical features include dysuria, urinary frequency, urgency, suprapubic pain or tenderness, and microscopic/macroscopic haematuria. Systemic symptoms (fever, chills, rigors, flank pain) are characteristically absent.
• Acute Pyelonephritis (Upper UTI): Infection of the renal pelvis and parenchyma. Characterised by acute systemic toxicity with high fever (> 38°C), shaking rigors, nausea, vomiting, severe unilateral loin/flank pain, and marked costovertebral angle tenderness (renal angle tenderness).

NICE Antimicrobial Prescribing Protocols

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2. Nephrolithiasis & Ureteric Calculi (Renal Colic)

Nephrolithiasis develops when urinary solutes exceed solubility saturation, resulting in crystal nucleation, aggregation, and stone formation. Types of calculi include:

• Calcium Oxalate (70–80%): Radio-opaque; promoted by hypercalciuria, hyperoxaluria, and hypocitraturia.
• Calcium Phosphate (10%): Radio-opaque; associated with primary hyperparathyroidism and distal Renal Tubular Acidosis (Type 1, high urinary pH).
• Uric Acid (5–10%): Radiolucent on plain X-rays (visible on CT); promoted by persistently acidic urine (pH < 5.5) and hyperuricaemia (gout, myeloproliferative disorders).
• Struvite (Triple Phosphate / Magnesium Ammonium Phosphate) (5–10%): Moderately radio-opaque; form large staghorn calculi filling the renal pelvicalyceal system secondary to urease-producing bacterial infections (Proteus, Klebsiella).
• Cystine (1%): Faintly radio-opaque; caused by autosomal recessive cystinuria.

Clinical Presentation

Classical renal colic is characterized by the sudden onset of excruciating, sharp, spasmodic loin-to-groin pain radiating across the ipsilateral flank toward the iliac fossa, scrotum, or labia majora. Patients are visibly restless, pacing or writhing on the bed unable to find a comfortable posture (contrasting with peritonitis, where patients lie rigidly motionless). Non-visible (microscopic) haematuria is present on dipstick in >90% of cases.

Diagnostic Imaging & Acute Analgesia

• Gold Standard Imaging: Non-contrast low-dose CT KUB (Kidney, Ureter, Bladder) performed within 24 hours of presentation (NICE NG118). Low-dose CT has >99% sensitivity and specificity, detecting calculi of all compositions (including radiolucent uric acid stones) and precisely measuring stone diameter and skin-to-stone distance.
• Pregnancy & Paediatrics: Renal tract ultrasound is first-line imaging to avoid ionising radiation.
• First-Line Analgesia: Intravenous or rectal Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), such as rectal diclofenac (100 mg) or IV ketorolac (15–30 mg). NSAIDs directly inhibit renal prostaglandin synthesis, reducing renal blood flow and glomerular filtration, thereby decompressing the renal capsule and halting ureteric smooth muscle spasm. Clinical trials confirm NSAIDs provide faster, more effective pain relief with fewer side effects than opioids. Intravenous paracetamol or opioids (morphine with antiemetic) are reserved for patients with strict NSAID contraindications (severe renal impairment, active peptic ulceration, third-trimester pregnancy, NSAID-exacerbated respiratory disease).

Definitive Stone Management by Size

                                [ Ureteric Calculus Identified on CT KUB ]
                                                    │
                         ┌──────────────────────────┴──────────────────────────┐
                         ▼                                                     ▼
            [ Calculus < 5 mm Diameter ]                              [ Calculus >= 5 mm Diameter ]
            • Spontaneous passage in >80-90%                          • Lower spontaneous passage rate
            • Outpatient conservative management                      • Assess for intervention
            • Oral analgesia & hydration                                       │
            • Medical Expulsive Therapy (MET):                        ┌────────┴────────┐
              Tamsulosin 400 mcg OD                                   ▼                 ▼
                         │                                    [ 5 - 10 mm ]       [ > 10 mm or Staghorn ]
            ┌────────────┴────────────┐                       Trial of MET or     Active Surgical Clearance:
            ▼                         ▼                       Early ESWL / URS    • URS + Holmium Laser
    [ Stone Passes ]         [ Persistent Pain / ]                                • PCNL (>20 mm staghorn)
    Follow-up complete       [ Failure to pass at 4w ]
                             Escalate to ESWL / URS

• Medical Expulsive Therapy (MET): Oral tamsulosin 400 mcg daily (an alpha-1 adrenoceptor antagonist) relaxes smooth muscle in the distal ureter, accelerating stone expulsion and reducing recurrent analgesic requirements for stones < 10 mm.
• Extracorporeal Shock Wave Lithotripsy (ESWL): Acoustic shock waves focus under fluoroscopy to fragment stones into passable gravel. Ideal for renal or upper ureteric calculi < 20 mm. Contraindicated in pregnancy, untreated UTI, and bleeding diathesis.
• Ureteroscopy (URS) with Laser Lithotripsy: Endoscopic visual clearance with holmium laser fragmentation and basket extraction; first-line for lower/mid ureteric stones and stones > 10 mm.
• Percutaneous Nephrolithotomy (PCNL): Direct percutaneous nephrostomy tract creation into the renal pelvis. Gold standard for large staghorn calculi (> 20 mm) or complex lower pole renal stones.

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3. Acute Urinary Retention: Assessment & Catheterisation Protocols

Acute Urinary Retention (AUR) is the sudden, painful inability to void urine, accompanied by marked suprapubic distress and an exquisitely tender, palpable bladder that is dull to percussion.

Clinical Classification & Common Aetiologies

• Prostatic Enlargement: Benign Prostatic Hyperplasia (BPH) is the underlying cause in >70% of male cases; prostate adenocarcinoma.
• Pharmacological Causes: Very common in hospitalised elderly patients. Anticholinergic / antimuscarinic agents (oxybutynin, tolterodine), tricyclic antidepressants (amitriptyline), opioids (morphine, oxycodone), first-generation antihistamines (chlorphenamine), and nasal decongestants (pseudoephedrine).
• Urethral Pathology: Urethral strictures, bladder neck contractures, urethral foreign body, clot retention (gross haematuria with obstructive luminal clots).
• Neurological: Cauda equina syndrome (always check perineal sensation, digital rectal examination for anal tone, and lower limb neurology), acute spinal trauma, multiple sclerosis, diabetic cystopathy.
• Other Triggers: Severe constipation / faecal impaction, post-operative anaesthesia, acute prostatitis, genital herpes.

Immediate Emergency Management Protocol

1. Immediate Urethral Catheterisation: Perform urgent bladder decompression using a 12–14 Fr Foley catheter under sterile conditions with generous instillation of lubricating local anaesthetic gel. Document the immediate residual urine volume (typically 500–1500 mL). Completely drain the bladder immediately; historical practice of clamping the catheter to prevent ex vacuo haematuria is obsolete and unsafe.
2. Failed Catheterisation: If resistance is encountered (e.g. stricture or false passage), do not use force. Contact urology immediately for flexible cystoscopy or urgent suprapubic catheter insertion.
3. Initiate Alpha-Blocker Therapy: Prescribe tamsulosin 400 mcg once daily immediately. Tamsulosin relaxes prostatic smooth muscle and doubles the likelihood of a successful Trial Without Catheter (TWOC).
4. Trial Without Catheter (TWOC): Attempt catheter removal after at least 48 to 72 hours of alpha-blocker therapy.
5. Monitor for Post-Obstructive Diuresis: Occurs after relieving chronic retention. Defined as urine output > 200 mL/hour for ≥ 2 consecutive hours. Monitor fluid balance, electrolytes, and replace 50% of hourly urine volume with IV 0.45% or 0.9% normal saline to prevent vascular collapse while allowing physiological excretion of retained solutes.