Urinary Tract Calculi

Key points

• • Urinary stones form when substances in the urine, such as calcium, oxalate and uric acid, become concentrated and crystallise.
• • Most stones contain calcium, and they form more easily when the urine is concentrated, so a low fluid intake is a key risk.
• • A stone passing down the ureter causes severe, colicky loin-to-groin pain (renal colic), often with blood in the urine.
• • A stone may block the flow of urine and, if infection is added, threaten the kidney.
• • Stones are shown by imaging, most sensitively by a CT scan, and many small ones pass on their own.