Key Facts

Renal stones are common and recurrent. Prevention through dietary modification and increased fluid intake is key to reducing recurrence, which occurs in 50% within 5 years.

Epidemiology

• Lifetime prevalence: 10-15% in UK; increasing incidence
• M:F 3:1 (gap narrowing)
• Peak age: 30-50 years
• Recurrence rate: 50% within 5 years, 80% within 10 years

Aetiology

Stone types:

• Calcium oxalate (70-80%): most common; radiopaque
• Calcium phosphate (10-15%): often mixed with oxalate
• Uric acid (5-10%): radiolucent on X-ray; associated with gout, acidic urine
• Struvite/triple phosphate (5-10%): "infection stones" (Proteus, Klebsiella); form staghorn calculi
• Cystine (1-2%): hexagonal crystals; autosomal recessive cystinuria

Pathophysiology

• Supersaturation of urine with stone-forming substances
• Nucleation → crystal growth → aggregation → stone formation
• Inhibitors of crystallisation: citrate, pyrophosphate, Tamm-Horsfall protein
• Risk factors: dehydration, high-sodium diet, animal protein, low fluid intake, hot climate, CKD, RTA, hyperparathyroidism

Acute Presentation (Ureteric Colic)

• Sudden-onset severe colicky pain: loin → groin (follows dermatomes T10-L2)
• Pain comes in waves; patient often writhing/unable to lie still
• Haematuria (microscopic or macroscopic; present in 85%)
• Nausea and vomiting
• Referred pain: testicular/labial if distal ureter

Location-Specific Features

• PUJ stones: loin pain
• Mid-ureter: radiates to flank/iliac fossa
• Vesicoureteric junction: frequency, urgency, suprapubic pain
• Bladder stones: intermittent stream, strangury

Complicated Stones

• Infected obstructed kidney: fever + loin pain + sepsis (EMERGENCY – requires immediate drainage)
• Staghorn calculus: large branching stone filling renal pelvis and calyces
• Bilateral obstruction or single kidney: AKI

Red Flags

• Fever + loin pain + urinary obstruction → pyonephrosis → emergency nephrostomy
• Bilateral stones with AKI → urgent urology
• Anuria → complete obstruction → urgent intervention

Bedside

• Urinalysis: haematuria (85%), nitrites/leucocytes if infection
• Pregnancy test: women of childbearing age (before CT)
• Observations: NEWS2 (sepsis assessment)

Bloods

• FBC, CRP: infection markers
• U&Es: renal function (AKI if obstructed)
• Calcium: hypercalcaemia (hyperparathyroidism)
• Urate: hyperuricaemia (uric acid stones)
• Blood cultures: if febrile

Imaging

• Non-contrast CT KUB: gold standard (>95% sensitivity/specificity); reveals stone size, location, hydronephrosis
• KUB X-ray: first-line in some centres; identifies radiopaque stones (calcium, struvite); misses uric acid and cystine
• Renal USS: alternative in pregnancy and children; detects hydronephrosis but limited stone detection

Special Tests

• Stone analysis: send passed/retrieved stones for composition analysis
• Metabolic workup (recurrent stone formers): serum calcium, PTH, urate, bicarbonate; 24h urine collection (calcium, oxalate, citrate, urate, creatinine, pH, volume)
• Cystine screen: spot urine cystine in young patients

Acute Management (NICE NG118)

• Analgesia: diclofenac 75mg IM or 100mg PR (first-line; superior to opioids for renal colic)
  • IV paracetamol as adjunct
  • Avoid NSAIDs in AKI, pregnancy, or peptic ulcer disease → morphine 10mg IM/IV alternative
• Antiemetics: ondansetron 4mg IV or metoclopramide 10mg IV
• IV fluids: if dehydrated or vomiting; NOT forced diuresis
• Medical expulsive therapy: tamsulosin 400mcg OD for distal ureteric stones 5-10mm (up to 4 weeks)

Intervention Criteria

• Stone >10mm unlikely to pass → intervention
• Stone not passed after 4 weeks
• Persistent pain despite analgesia
• Infected obstructed system → emergency nephrostomy/stent
• Bilateral obstruction or single kidney

Interventional Options

• ESWL: first-line for renal stones <20mm; non-invasive
• Ureteroscopy (URS): preferred for ureteric stones; allows laser lithotripsy
• PCNL (percutaneous nephrolithotomy): for large renal stones >20mm or staghorn calculi
• Open/laparoscopic surgery: rarely needed

Prevention of Recurrence

• Fluid intake: ≥2.5L/day (target urine output >2L/day)
• Dietary: reduce sodium (<6g/day), moderate animal protein, normal calcium intake (low calcium paradoxically increases oxalate stones)
• Calcium oxalate stones: potassium citrate (alkalinises urine, inhibits crystallisation)
• Uric acid stones: allopurinol 100-300mg OD + potassium citrate (target urine pH 6.5-7.0)
• Cystine stones: high fluid intake (>3L/day) + potassium citrate ± D-penicillamine/tiopronin
• Struvite stones: treat underlying infection; complete stone clearance essential

Referral Criteria

• Stone >5mm not passing → urology
• Recurrent stones → metabolic workup
• Infected obstructed kidney → emergency urology

• Stones <5mm: 80-90% pass spontaneously within 4 weeks
• Stones 5-10mm: ~50% pass spontaneously
• Stones >10mm: <10% pass spontaneously
• Recurrence: 50% within 5 years without preventive measures; reduced to 10-15% with lifestyle modifications
• ESWL success rate: 70-90% for stones <20mm
• Ureteroscopy success rate: 90-95% for ureteric stones
• Staghorn calculi: if untreated, can cause loss of kidney function and sepsis

Stone Types Summary

Metabolic Causes to Investigate