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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Lifetime prevalence ~10%. Commonest stone type: calcium oxalate (~75%). Others: uric acid, struvite (infection/Proteus), cystine
- Ureteric colic: severe colicky loin-to-groin pain, often with nausea/vomiting. Patient typically cannot lie still (unlike peritonitis)
- Gold standard investigation: non-contrast CT KUB (sensitivity/specificity >95%)
- Analgesia: IM/IV diclofenac (first-line), NOT opioids initially. Medical expulsive therapy (alpha-blocker) for stones 5–10 mm
- Stones ≤5 mm: usually pass spontaneously (~90%). Stones >10 mm: likely need intervention (ESWL, ureteroscopy, or PCNL)
Overview
Renal calculi (kidney stones) form when urinary concentrations of stone-forming substances exceed their solubility. The commonest type is calcium oxalate (~75%), followed by calcium phosphate (~15%), uric acid (~5–10%), struvite (~5% — associated with urease-producing organisms like Proteus), and cystine (<1% — inherited disorder). Risk factors include dehydration, high dietary sodium/protein/oxalate, hypercalciuria, hyperparathyroidism, family history, obesity, CKD, recurrent UTIs, and certain medications (loop diuretics, topiramate). Stones typically cause symptoms when they obstruct the ureter, causing intense colicky pain (renal or ureteric colic).
Epidemiology
Renal calculi have a lifetime prevalence of approximately 10% in the UK, with a recurrence rate of ~50% within 5–10 years. They are 2–3 times more common in males. Peak incidence is between ages 30 and 50. Incidence is increasing, attributed to rising obesity and dietary changes. Approximately 100,000 presentations to UK emergency departments per year. Most small stones (<5 mm) pass spontaneously; larger stones often require intervention.
Clinical Features
Symptoms
Severe colicky loin/flank pain radiating to groin, testicle, or labia (follows ureteric course)
Pain comes in waves (ureteric peristalsis against obstruction)
Nausea and vomiting (vagal stimulation)
Haematuria (macro or microscopic — absent in ~15% despite stone)
Urinary frequency and urgency (if stone at vesicoureteric junction)
Restlessness — patient cannot find a comfortable position (distinguishes from peritonitis where patient lies still)
Fever and rigors (infected obstructed kidney — urological emergency)
Signs
Renal angle tenderness
Patient writhing in pain (cannot lie still)
Tachycardia (pain-related)
Fever (infected stone/pyonephrosis)
Abdominal examination usually soft with no peritonism
Investigations
First-line
Non-contrast CT KUBGold standard — sensitivity and specificity >95% for ureteric stones. Shows stone location, size, and degree of obstruction (hydronephrosis). Identifies ALL stone types except indinavir stones
UrinalysisHaematuria (absent in ~15%). Dipstick for nitrites/leucocytes (exclude infection). pH: persistently alkaline → struvite; persistently acidic → uric acid
BloodsU&Es (renal function, AKI if bilateral obstruction or solitary kidney), FBC, CRP (infection), calcium (hypercalcaemia/hyperparathyroidism), uric acid
Second-line
Stone analysisStrain urine and send passed stone for compositional analysis — guides prevention strategy
USS KUBFirst-line in pregnancy (no radiation) and children. Can detect hydronephrosis but less sensitive for ureteric stones
Metabolic stone screen (if recurrent)24-hour urine collection: calcium, oxalate, uric acid, citrate, cystine, sodium, pH, volume. Serum PTH, calcium, phosphate
Specialist
CT IVU or IVUIf anatomical detail needed for surgical planning — rarely needed now with CT KUB
1
Acute pain management
- First-line: IM or IV diclofenac 75 mg (or PR 100 mg) — more effective than opioids for renal colic (NICE NG29)
- Second-line: IV paracetamol 1 g if NSAID contraindicated
- Third-line: IV morphine if refractory pain (avoid if possible — less effective and more side effects)
- Antiemetic: ondansetron or cyclizine
2
Conservative management
- Stones ≤5 mm: ~90% pass spontaneously. Watchful waiting with analgesia and high fluid intake
- Stones 5–10 mm: medical expulsive therapy (MET) — tamsulosin 400 µg OD (alpha-blocker, relaxes ureteric smooth muscle) may facilitate passage
- Advise straining urine to catch stone for analysis
- Follow-up imaging to confirm stone passage
3
Interventional treatment
- Stones >10 mm (or failed conservative/complicated): require intervention
- ESWL (extracorporeal shockwave lithotripsy): for renal stones <20 mm and proximal ureteric stones. Non-invasive, outpatient
- Ureteroscopy (URS) with laser lithotripsy: for ureteric stones. Rigid or flexible. Can be diagnostic and therapeutic
- PCNL (percutaneous nephrolithotomy): for large renal stones >20 mm or staghorn calculi. Requires general anaesthesia
4
Emergency intervention
- Infected obstructed kidney (pyonephrosis): urological EMERGENCY — urgent decompression with nephrostomy or ureteric stent + IV antibiotics
- Bilateral obstruction or obstruction of solitary kidney: urgent drainage to prevent/treat AKI
- Urosepsis: Sepsis 6 + urgent drainage
5
Prevention of recurrence
- High fluid intake (>2.5 L/day — aim for urine output >2 L/day)
- Reduce dietary sodium and animal protein
- Calcium oxalate stones: normal dietary calcium (do NOT restrict), reduce oxalate (spinach, rhubarb, nuts, chocolate)
- Uric acid stones: alkalinise urine (potassium citrate) ± allopurinol
- Cystine stones: high fluid intake + alkalinise urine + tiopronin/D-penicillamine
- Struvite stones: treat underlying UTI, complete stone clearance essential
Complications
- Ureteric obstruction: Hydronephrosis → AKI (especially if bilateral or solitary kidney)
- Infected obstructed kidney (pyonephrosis): Urological emergency — requires urgent drainage
- Urosepsis: From infected stone → septic shock
- Ureteric stricture: From chronic impaction or post-intervention
- Recurrence: ~50% recurrence within 5–10 years without preventive measures
UKMLA Exam Tips
- 1Diclofenac (NSAID) is FIRST-LINE analgesia for renal colic — more effective than opioids (NICE NG29)
- 2Non-contrast CT KUB is the gold standard. USS is first-line only in pregnancy and children
- 3Calcium oxalate stones: most common (~75%). Radio-OPAQUE on X-ray. Do NOT restrict dietary calcium (paradoxically increases oxalate absorption)
- 4Uric acid stones: RADIOLUCENT on X-ray (visible on CT but NOT on plain film). Dissolve with urine alkalinisation
- 5Struvite (magnesium ammonium phosphate) = INFECTION stones (Proteus). Form staghorn calculi. Need complete clearance + treat infection
- 6Cystine stones: autosomal recessive cystinuria. Hexagonal crystals on microscopy. Positive cyanide nitroprusside test
- 7Infected obstructed kidney = EMERGENCY. Antibiotics ALONE will not work — must drain (nephrostomy or stent)
- 8Restless patient writhing in pain = renal colic. Still patient afraid to move = peritonitis
practicetest your knowledge on renal calculiApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — renal and beyond.
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