Explainer · 6 min read
Kidney stones: why they form, how to keep them away
Kidney stones can cause sudden, severe loin pain, nausea, blood in the urine and repeated hospital visits. Treatment is not just about removing one stone; it is about understanding why it formed and reducing the chance of another one.
How kidney stones form
Stones form when minerals in urine become too concentrated and crystallise. Low fluid intake, high salt intake, recurrent infections, family history, bowel conditions, some medications and metabolic factors can all contribute. The most common stones contain calcium, but calcium in the diet is not usually the enemy. In many patients, excess salt, low urine volume and specific urine chemistry are more important.
Symptoms and diagnosis
A stone in the kidney may cause no symptoms. Pain often begins when a stone moves into the ureter, the narrow tube between kidney and bladder. Classic renal colic causes waves of severe loin pain that may travel to the groin. Blood in the urine, urinary frequency, nausea and sweating are common. A CT scan is often the most accurate test for size and position, although ultrasound and X-ray may be useful in selected cases.
Will the stone pass by itself?
The chance of passing a stone depends mainly on size, location, symptoms, infection risk and kidney function. Small lower ureteric stones may pass with pain relief, fluids and sometimes medication to relax the ureter. Larger stones, persistent pain, infection, reduced kidney function or stones that are not moving usually need active treatment.
Treatment options
- Observation: suitable for some small stones when pain is controlled and there is no infection.
- Shockwave lithotripsy: external shockwaves break selected stones into fragments that can pass naturally.
- Ureteroscopy and laser: a fine scope passes through the bladder into the ureter or kidney, and a laser fragments the stone.
- Mini-PCNL: keyhole surgery through the back for larger or more complex kidney stones.
- Stent insertion: used to unblock the kidney urgently or protect drainage around treatment.
What to expect from ureteroscopy
Ureteroscopy is commonly performed as a day-case procedure under anaesthetic. No skin incision is needed. A laser breaks the stone, and fragments may be removed or left as dust to pass. A temporary ureteric stent is sometimes placed to help drainage while swelling settles. Stents can cause frequency, urgency, flank discomfort and blood in the urine, but these symptoms usually improve after removal.
Preventing another stone
Prevention starts with urine volume. Many recurrent stone formers are not drinking enough to produce dilute urine throughout the day. A practical aim is pale urine most of the time, unless another doctor has restricted fluids. Salt reduction is also important because high salt can increase calcium loss into urine. Crash diets, very high animal-protein intake and dehydration during exercise or travel can increase risk.
- Drink steadily across the day, more in hot weather or after sweating.
- Reduce salt and processed foods.
- Keep normal dietary calcium unless specifically advised otherwise.
- Increase fruit and vegetables where appropriate.
- Ask whether stone analysis and a metabolic urine test are needed.
When a metabolic stone clinic helps
Recurrent stones, bilateral stones, young age at first stone, unusual stone type, kidney impairment or strong family history are reasons to look deeper. A metabolic assessment can identify low urine volume, high calcium, high oxalate, low citrate, uric acid risk or infection stone patterns. Prevention can then be targeted rather than generic.
Questions to bring to your appointment
- Where exactly is my stone and how large is it?
- Is my kidney draining safely?
- What are the chances of passing it without surgery?
- Would shockwave, ureteroscopy or mini-PCNL be most suitable?
- How do we prevent another stone after this one is treated?
Further reading from BAUS
The British Association of Urological Surgeons publishes peer-reviewed patient leaflets that go into more detail than this overview.
This guide is general information only and does not replace personalised medical advice. If stone pain is associated with fever, vomiting or feeling very unwell, seek urgent care.