What causes kidney stones?

Kidney stones (also known as renal calculi or nephrolithiasis) are hard deposits composed of minerals and salts formed within the kidney. Kidney stones can affect any part of the urinary tract, from the kidneys through to the bladder.

Kidney stones are a common condition and affect 2-3% of the general population. They are more prevalent in men than in women.

Kidney stones vary in size. They can start as small as a grain of sand but can grow as large as a pebble.  Some stones stay in the kidney while others may travel down the ureter.

Kidney stones form when your urine contains a higher level of crystal forming substances, such as calcium, oxalate and uric acid, than the fluids in your urine can dilute. Your urine may also lack substances that prevent crystals from sticking together, creating an ideal environment for them to form.

Different types of kidney stones are made of different chemicals, and these include:

• Calcium stones – This is the most common type of kidney stone and usually develop due to excessive calcium oxalate, which is found in certain fruits, vegetables, nuts and chocolates.
• Uric acid stones – This type of kidney stone normally develops due to chronic dehydration, a diet too high in protein or in those with gout.
• Struvite stones – These are less common and form in response to certain types of urinary tract infections, where bacteria makes ammonia that builds up in the urine. Struvite stones can grow quickly and become quite large.
• Cystine stones – These are found in people with genetic disorders that cause cystine to leak from the kidneys into the urine.

The following can increase your risk of having kidney stones:

• Had kidney stones before
• Family history of kidney stones
• Dehydration
• Diets high in animal protein, sodium (salt) and sugar
• Obesity
• Urinary tract infections
• Polycystic kidney disease
• Metabolic diseases (e.g. gout, hyperparathyroidism and renal tubular acidosis)
• Certain medications and supplements (e.g diuretics or calcium- based antacids, vitamin C supplements or excessive use of laxatives)
• Digestive diseases and gastric surgery

Very small kidney stones that move easily through the urinary tract may not cause any symptoms, so many people are not aware that they have kidney stones.

However, when the kidney stone starts to move around within the kidney, passes into the ureters or gets stuck in the ureters, this may block the flow of urine. This causes the kidneys to swell and ureter to spasm which can be very painful. The pain may also shift in location as the stone moves through the urinary tract.

You may experience:

To determine if you have kidney stones, imaging of the urinary tract will be required including:

• X-ray
• Ultrasound kidneys and bladder
• IVU (intravenous urogram)
• CT scan (computerised tomography) – this is the gold standard for detection of kidney stones as it can pick up very small stones

Additional tests may include:

• Blood tests to detect the amount of calcium and uric acid in your blood.
• Urine tests, involving a 24-hour urine collection, to measure urine volume and levels of chemicals in the urine that can cause the stones.

Treatment varies for kidney stones depending on your symptoms, health and the size and location of the stone.

Most kidney stones do not require invasive treatment.

For most small kidney stones, management includes:

• Drinking plenty of water (at least 2-3 litres a day) to flush out the stone
• Pain relief medications, if required
• Medication to assist in stone expulsion may be given. This medication relaxes the muscles in the ureter and will help you pass the kidney stone quickly and with less pain.

For larger stones, options for treatment include:

• Medication – To help break down the stones, the type of medication given will depend on the type of stone.
• Extracorporeal shock wave lithotripsy (ESWL) – A non-invasive procedure where ‘shock waves’ are used to break up stones into small pieces, which will then be passed out in the urine over the next few days.

For stones that are too large to pass out naturally, in an awkward position or causing significant pain, surgical treatment may be needed. This includes:

• Ureteroscopy – This procedure uses a long scope with a camera at the end which is inserted through the urethra into the urinary passage leading up to the stone. The stone is then broken into smaller pieces and fragments are removed.
• PCNL (percutaneous nephrolithomy) – A surgical treatment that involves making a small incision in the back (or loin) and inserting a special instrument into the kidney to locate and remove the stones.
• Open surgery – A large incision is made through which the stone is removed. This is seldom necessary nowadays unless the stone is very large and complex.

To prevent kidney stones it is important to:

• Drink enough water every day (about 2.5 litres a day). In general you should drink enough water to make your urine clear and colourless
• Eat fewer oxalate-rich foods and if you tend to form calcium oxalate stones, you should decrease your intake of nuts, tea and chocolate
• Have a diet low in salt and animal protein (e.g. meat and eggs)
• You can continue eating calcium-rich foods, but use caution with calcium supplements

Stones recur in up to 50% of patients. Therefore, take the necessary precautions and have regular check-ups to reduce your risk of kidney stones and ensure they are detected early.