Kidney stones (nephrolithiasis or urolithiasis) form when minerals and salts crystallise in the kidneys. The pain of a stone passing through the ureter is notoriously severe — but diagnosis and treatment decisions depend on a combination of clinical assessment, imaging and blood and urine tests.
Imaging tests
- CT scan (KUB — kidney, ureter, bladder) — the gold standard; detects virtually all stones regardless of composition; no contrast needed
- Ultrasound — identifies larger stones and hydronephrosis (kidney swelling); misses small stones in the ureter; preferred in pregnancy to avoid radiation
- Plain X-ray (KUB) — only detects calcium-containing stones; less used now that CT is widely available
Blood and urine tests
- Full blood count — checks for infection (raised white cells) and anaemia
- Creatinine and eGFR — assesses kidney function; essential before and after any obstruction
- Calcium, uric acid — raised levels are risk factors for certain stone types
- Urine dipstick — looks for blood (almost always present with a stone), infection and pH
- 24-hour urine collection — for recurrent stone-formers; measures stone-forming minerals and their inhibitors to guide prevention
- Stone analysis — if a stone passes or is retrieved, laboratory analysis of its composition guides prevention strategy
What happens next
Small stones (under 5 mm) typically pass spontaneously within 2–4 weeks with adequate hydration and pain management. Larger stones, obstructing stones causing kidney damage, or stones in the setting of infection require urological intervention — shockwave lithotripsy, ureteroscopy or, less commonly, surgery.