Key Facts

Renal stone disease (urolithiasis) is one of the most common urological conditions, causing significant morbidity and healthcare resource utilisation. It is characterised by the formation of crystalline deposits within the urinary tract.

Epidemiology

Lifetime prevalence is approximately 10-15% in the UK, with male-to-female ratio of 3:1 (narrowing). Peak incidence is at 30-50 years. Prevalence is increasing, linked to rising obesity and dietary changes. Stone disease accounts for approximately 1-2% of all emergency department attendances.

Aetiology

Stone composition:

• Calcium oxalate (70-80%): Hypercalciuria, hyperoxaluria, hypocitraturia
• Calcium phosphate (10-15%): Associated with RTA type 1, hyperparathyroidism
• Uric acid (5-10%): Gout, myeloproliferative disorders, acidic urine
• Struvite/MAP (5-10%): UTI with urease-producing organisms (Proteus, Klebsiella)
• Cystine (1-2%): Autosomal recessive cystinuria

Pathophysiology

Stones form when urine becomes supersaturated with stone-forming salts. Factors promoting crystallisation include low urine volume, high solute concentration, low citrate (an inhibitor), and urine pH extremes. Calcium oxalate crystallises at normal pH, uric acid at low pH (<5.5), and calcium phosphate at high pH. Stones cause pain through ureteric obstruction, smooth muscle spasm, and mucosal inflammation.

Acute Renal Colic

• Sudden-onset severe colicky loin pain radiating to the groin/testis/labia
• Patient unable to find a comfortable position (writhing)
• Nausea and vomiting
• Visible or non-visible haematuria (present in ~80%)

Stone Location and Symptoms

• Renal pelvis/upper ureter: Loin pain, costovertebral angle tenderness
• Mid-ureter: Pain radiating to flank and abdomen
• Lower ureter/VUJ: Pain radiating to groin, frequency, urgency
• Bladder stones: Suprapubic pain, terminal haematuria, interrupted stream

Red Flags

• Infected obstructed kidney (pyonephrosis): Fever + loin pain + obstructed system — urological emergency requiring emergency nephrostomy/ureteric stent
• Bilateral ureteric obstruction or obstruction of a solitary kidney — acute kidney injury
• Stone >10mm unlikely to pass spontaneously — consider early intervention
• Anuria — complete bilateral obstruction

Bedside

• Urine dipstick: Haematuria (present in ~80%), leucocytes/nitrites (infection)
• Temperature: Fever suggests infected stone — emergency
• Pain assessment: Visual analogue scale

Bloods

• FBC: WCC elevated if infection
• U&Es: Renal function — important if bilateral obstruction or solitary kidney
• CRP: Raised in infection
• Calcium: Screen for hyperparathyroidism
• Urate: Screen for gout/uric acid stones

Imaging

• CT KUB (non-contrast): Gold standard — sensitivity >95%, specificity >98%. Identifies stone size, location, and number
• USS: First-line in pregnancy and children; detects hydronephrosis but may miss ureteric stones
• KUB X-ray: Follow-up of known radio-opaque stones (calcium). Uric acid and cystine stones are radiolucent

Special Tests

• Stone analysis: Submit all passed/retrieved stones for biochemical analysis
• 24-hour urine collection: For recurrent stone formers — calcium, oxalate, urate, citrate, cystine, volume
• Metabolic screen: PTH if hypercalcaemia, cystine screen if young patient with recurrent stones

Non-pharmacological

• Increase fluid intake: Aim for urine output >2.5L/day
• Dietary advice: Reduce sodium, animal protein; normal calcium intake (not restricted); increase citrate-rich foods
• Strain urine: To capture passed stone for analysis

Pharmacological

• Acute pain relief: Diclofenac 75mg IM (first-line per NICE) or PR 100mg; paracetamol 1g IV; morphine 10mg SC/IV if needed
• MET: Tamsulosin 400mcg OD for distal ureteric stones 5-10mm (limited evidence but widely used)
• Recurrence prevention: Potassium citrate (uric acid and calcium stones), thiazide diuretics (hypercalciuria), allopurinol 100-300mg OD (uric acid), tiopronin/D-penicillamine (cystine)
• Urinary alkalinisation: Potassium citrate to maintain urine pH 6.5-7.0 for uric acid stone dissolution
• Antibiotics: If infected stone — IV co-amoxiclav 1.2g TDS or gentamicin + amoxicillin per local protocol

Surgical/Interventional

• Ureteric stenting/nephrostomy: Emergency drainage for infected obstructed system
• SWL (shockwave lithotripsy): First-line for renal stones <20mm and ureteric stones <10mm
• Ureteroscopy (URS): Flexible or rigid; laser lithotripsy — first-line for ureteric stones 10-20mm
• PCNL (percutaneous nephrolithotomy): First-line for renal stones >20mm or staghorn calculi
• Open/laparoscopic surgery: Rarely needed; reserved for complex cases

Referral Criteria

• Infected obstructed kidney — emergency urology
• Stone >10mm or failure of conservative management — urology referral
• Recurrent stones — metabolic workup and stone clinic
• Bilateral obstruction/solitary kidney obstruction — emergency

• Spontaneous passage rates: <5mm: 90%; 5-10mm: 50%; >10mm: <10%
• Recurrence: ~50% within 5 years, ~70% within 10 years without preventive measures
• Stone-free rates after intervention: SWL 70-85% (size dependent), URS 90-95%, PCNL 85-95%
• Infected obstructed kidney (pyonephrosis): Mortality up to 10% if not urgently drained
• CKD risk: Recurrent stones increase risk of CKD; bilateral staghorn calculi can cause ESRD

Stone Composition and Features

Management Algorithm by Stone Size