Kidney stones, medically known as renal calculi or urinary stones, are hard deposits that form within the urinary system when substances naturally present in urine become concentrated and crystallise. They are common and can affect anyone, although some people are more prone to developing stones because of their diet, fluid intake, genetics, medical conditions or urinary tract anatomy.
While some kidney stones remain within the kidney without causing problems, others can move into the ureter and cause severe pain, obstruction or infection. Modern minimally invasive treatments mean that most stones can now be treated effectively without open surgery.
Mr Gidon Ellis is a Consultant Urological Surgeon specialising in endourology and kidney stone management. He provides assessment and treatment for kidney stones, including ureteroscopy and ESWL, and works closely with specialist stone surgeons for complex procedures such as PCNL when required.
What are kidney stones?
Kidney stones are solid crystals that form when certain substances in urine become too concentrated. Urine normally contains substances that help prevent crystal formation, but when this balance changes, crystals can develop and gradually grow into stones.
Kidney stones may be:
- Very small and pass unnoticed
- Large enough to obstruct urine drainage
- Multiple stones affecting one or both kidneys
Stones can occur anywhere within the urinary tract:
- Kidney (renal stone)
- Ureter (ureteric stone)
- Bladder (less commonly)
What causes kidney stones?
There is rarely a single cause. Kidney stones usually develop because of a combination of factors.
Low fluid intake
Not drinking enough water causes urine to become more concentrated, increasing the chance of crystal formation. Maintaining a good urine volume is one of the most important ways to reduce stone risk.
Dietary factors
Certain dietary factors can increase the risk of kidney stones, including:
- High salt intake
- Excess animal protein intake
- Low dietary calcium intake in some situations
- Dietary factors specific to the type of stone formed
A balanced diet with appropriate calcium intake is important, as unnecessarily restricting calcium can sometimes increase stone risk.
Metabolic factors
Some people naturally excrete higher levels of stone-forming substances in their urine, including:
- Calcium
- Oxalate
- Uric acid
Understanding these factors can be particularly important in patients who repeatedly form stones.
Medical conditions
Certain conditions can increase the likelihood of kidney stones, including:
- Gout
- Hyperparathyroidism
- Some bowel conditions affecting absorption
- Recurrent urinary infections
Family history
Some people have an inherited tendency to form kidney stones.
What types of kidney stones are there?
The type of kidney stone is important because it can provide clues about why the stone formed and help guide strategies to prevent future stones.
Calcium oxalate stones
Calcium oxalate stones are the most common type of kidney stone.
They form when calcium combines with oxalate in the urine. Factors that can contribute include:
- Low urine volume due to inadequate fluid intake
- Higher urinary oxalate levels
- Certain dietary factors
- Some metabolic conditions
Calcium phosphate stones
Calcium phosphate stones are another type of calcium-based kidney stone.
They are more likely to form when urine is less acidic (more alkaline) and may be associated with:
- Certain metabolic abnormalities
- Some kidney tubule disorders
- Overactive parathyroid glands (hyperparathyroidism)
Identifying calcium phosphate stones can be helpful because prevention strategies may differ from those used for calcium oxalate stones.
Uric acid stones
Uric acid stones form when urine is too acidic, allowing uric acid crystals to develop.
They may be associated with:
- Gout
- Metabolic syndrome
- Higher intake of animal protein
- Certain dietary patterns
Infection stones (struvite stones)
These stones develop in association with certain urinary tract infections. They can grow rapidly and may form large branching stones within the kidney (staghorn stones).
Cystine stones
Cystine stones are rare and occur due to an inherited condition called cystinuria, which affects how certain amino acids are handled by the kidneys.
What symptoms do kidney stones cause?
Kidney stones may cause no symptoms if they remain within the kidney. Symptoms usually occur when a stone moves into the ureter or blocks urine drainage.
Common symptoms include:
- Severe flank or back pain (renal colic)
- Pain radiating towards the groin
- Nausea or vomiting
- Blood in the urine
- Urinary urgency or frequency, particularly when the stone is close to the bladder
- Discomfort when passing urine
A stone causing obstruction alongside infection can be a medical emergency.
How are kidney stones diagnosed?
Diagnosis involves confirming the presence of a stone and understanding its size, location and impact on the urinary tract.
Urine testing
Urine tests can identify:
- Blood in the urine
- Infection
- Other abnormalities
Blood tests
Blood tests may assess:
- Kidney function
- Signs of infection
- Factors that may contribute to stone formation
CT KUB scan
A CT scan of the kidneys, ureters and bladder (CT KUB) is the most accurate investigation for many patients.
It provides important information about:
- Stone size
- Stone location
- Degree of blockage
- Likelihood of passing the stone naturally
Stone analysis
If a stone is removed or passed, analysing its composition can provide valuable information. Understanding whether a stone is calcium oxalate, calcium phosphate, uric acid or another type can help guide prevention strategies and reduce the risk of recurrence.
How are kidney stones treated?
Treatment depends on:
- Stone size
- Stone location
- Symptoms
- Presence of obstruction
- Presence of infection
- Patient preference
Observation
Small stones may pass naturally without intervention.
Management may include:
- Pain relief
- Monitoring
- Follow-up imaging
ESWL (shockwave lithotripsy)
ESWL uses focused shockwaves from outside the body to break stones into smaller fragments that can pass naturally.
Ureteroscopy
Ureteroscopy involves passing a small telescope through the urinary tract to directly visualise and treat stones. The stone is usually fragmented using a laser and removed.
PCNL
For larger or more complex kidney stones, PCNL may be recommended. This involves creating a small keyhole access into the kidney through the back to remove stones.
Can kidney stones come back?
Yes. Once someone has formed a kidney stone, they may be at increased risk of developing further stones.
The risk of recurrence depends on:
- The reason the stone formed
- Fluid intake
- Dietary factors
- Underlying metabolic abnormalities
- Whether preventative measures are introduced
Patients who develop repeated stones may benefit from specialist stone prevention assessment.
How can kidney stones be prevented?
Prevention depends on understanding why the stone formed.
General measures include:
Drinking enough fluid
Maintaining a high urine volume is one of the most important ways to reduce stone risk.
Dietary optimisation
Advice may include:
- Reducing salt intake
- Maintaining appropriate calcium intake
- Moderating excess animal protein intake
- Adjusting specific dietary factors depending on stone type
Metabolic assessment
Selected patients, particularly those with recurrent stones, may benefit from:
- Stone composition analysis
- Blood tests
- 24-hour urine collection
This allows prevention strategies to be tailored to the individual.
When should I seek medical advice?
You should seek assessment if you have:
- Suspected kidney stone pain
- Blood in the urine
- Recurrent urinary symptoms
- A known stone causing symptoms
Urgent assessment is required if you have:
- Fever or signs of infection
- Severe uncontrolled pain
- Persistent vomiting
- Difficulty passing urine
A blocked infected kidney requires urgent treatment to drain the kidney and control infection.
At a glance
| Also called | Renal calculi, urinary stones |
|---|---|
| Affects | Kidney and urinary tract |
| Common symptoms | Flank pain, blood in urine, nausea, urinary symptoms |
| Diagnosed with | CT KUB, urine tests, blood tests |
| Treatment options | Observation, ESWL, ureteroscopy, PCNL |
| Prevention | Hydration, dietary measures, metabolic assessment where appropriate |
Diagnosed with kidney stones?
Kidney stones are common but highly treatable. Specialist assessment can help determine the safest and most effective treatment approach and reduce the risk of future stones. Book a consultation to discuss your kidney stone diagnosis and treatment options.
