Passing a kidney stone is often said to be the worst pain that anyone can experience. Kidney stones are common, affecting approximately 1 in 5 men and 1 in 10 women by the age of 70.

How do kidney stones develop?

Kidney stones usually form when the urine concentration of substances such as calcium, oxalate, cystine or urate is high. This can be related to an underlying health or dietary issue but is often made worse by not drinking enough fluid.

Stones start as tiny crystals within the kidney which over years increase in size to form a kidney stone.

Stones often remain within the kidney for many years and cause no symptoms but if they dislodge and drop into the urinary tract problems can arise.

What are the risk factors for kidney stones?

Certain health problems and dietary habits increase the risk of kidney stones. The risk is also increased if other family members have had kidney stones or if you have previously had kidney stones.

Dietary factors

∎ Poor fluid intake (or living or working in hot environments)

∎ A diet with low levels of calcium

∎ High levels of animal protein

∎ High levels of sugar (sucrose, fructose)

∎ Low levels of phytate (found in wheat, rice, rye, barley and beans)

∎ A high sodium content

∎ A high spinach intake

∎ Use of calcium supplements

∎ Other medical conditions

∎ Primary hyperparathyroidism

∎ Gout

∎ Diabetes mellitus

∎ Obesity

∎ Inflammatory bowel disease

∎ Gastric or intestinal bypass surgery

What are the symptoms of kidney stones?

Kidney stones can stay within the kidney for many years and usually don’t cause any symptoms. However, symptoms are common if the stone dislodges and passes through the urinary tract.

Pain

This is very common when passing a kidney stone and is caused obstruction of the ureter. This is known as renal colic. Pain can be a vary from a mild ache to a pain that is so severe that it requires hospital treatment. The pain typically comes in waves and is felt between the flank and the groin.

Blood in the urine

Most people with kidney stones will have blood in the urine (haematuria). This may be obvious with the urine appearing pink or reddish, or it may be invisible and only detectable with dipstick testing.

Gravel

Some patients pass multiple small stones in the urine which appear as sand or gravel. Pain is usually minor.

Other symptoms

These include nausea, vomiting, pain on urination, and an urgent need to pass urine.

How are kidney stones diagnosed?

While the symptoms are often suggestive of kidney stones, the diagnosis depends on identifying stones on an imaging test.

CT (computed tomography) scan

This is the best method to identify stones. It is an X-ray scan that creates a detailed three-dimensional picture of structures within the body and can identify stones in the kidneys, ureters, and bladder.

Ultrasound

This is often able to detect stones in the kidneys or the bladder but it is not as good at picking up stones in the ureters. It is mainly used when X-rays are best avoided, for example in pregnant women.

How are kidney stones treated?

Treatment of kidney stones depends on their size and location, as well as the severity of the symptoms.

If the stone is small enough to be expected to pass

If pain is mild, and there is no vomiting, this can usually be treated at home with pain relief, and oral fluids until the stone passes. Medication, eg Flomax (tamsulosin), can encourage the stone to pass more quickly. Straining the urine allows the stone to be collected and then analysed – this can be helpful in preventing future stone formation.

If the pain is severe and is associated with nausea and vomiting, or if there is a fever, hospital treatment with stronger pain medications, intravenous fluids, and possibly antibiotics will be needed.

If the stone does not pass

Stones larger than 9mm or 10mm in diameter often do not pass and require a procedure to remove them. Several different treatment options are available:

Ureteroscopy

A thin telescope is passed through the urethra and bladder and into the ureter. The stone can then be either removed or broken up (usually with a laser) into pieces that can pass.

Shockwave lithotripsy (ESWL)

High-energy shock waves are targeted at the stone causing it to break into fragments. It is less effective for stones over 1cm or hard stones. Lithotripsy is often done with sedation to reduce discomfort.

Percutaneous nephrolithotomy (PCNL)

This is a “keyhole” surgical procedure in which a small telescope is passed through the skin of the back into the kidney to remove the stone. This is usually used for very large or complex stones, or stones that do not respond to lithotripsy or ureteroscopy.

If the stone is asymptomatic

A kidney stone that is causing no symptoms may not need to be removed immediately. The decision around treatment depends on the size and location of the stone, and the potential for future complications.

How can kidney stones be prevented?

If you have kidney stones, it is important to be evaluated to identify options to reduce the risk of future stone formation. This evaluation may include:

• Analysis of passed stones.

• Urine tests

• Other tests, including additional blood tests or further scans.

Depending on the underlying cause of the kidney stone there are a number of potential treatment options:

Increasing fluid intake

This is the most important part of treatment. Drinking more fluid lowers the risk of kidney stones by reducing the urine concentration of substances that cause stone formation. Aim for three litres (100 fl oz) intake a day. It is important to avoid sugar-sweetened beverages (soft drinks and sports drinks) as these promote kidney-stone formation.

Changing your diet

Dietary changes may be appropriate depending on the type of kidney stone or the results of the 24-hour urine collections.

Preventive medication

This may be advised in certain circumstances. For example, allopurinol for urate stones, thiazide diuretics for calcium stones.

• Peter Topham, MD, is a consultant nephrologist at the Bermuda Hospitals Board. He is also co-editor of the textbook Oxford Desk Reference: Nephrology