A kidney stone is a hard, stone-like mass that can form in one or both kidneys. Most people are born with two kidneys, organs that "clean" the blood. They filter out water and waste products, making urine.
Kidney stones are formed out of crystals found in the urine. In most cases, the crystals are too tiny to be noticed, and pass harmlessly out of the body. However, they can build up inside the kidney and form much larger stones.
If a stone grows big enough to block the flow of urine out of the kidney, it can cause pressure, pain, and infection. If a stone moves out of the kidney with the flow of urine, it can cause severe pain as it moves through the tubes that carry urine from the kidney to the bladder. If a stone gets stuck, an infection can arise. Depending on its size and position, an untreated kidney stone could cause permanent damage to the kidneys.
Kidney stones are fairly common. About 1% of people in Western countries are likely to get them.
Depending on where they are found, kidney stones are also known as renal calculi, urinary calculi, urinary tract stone disease, nephrolithiasis, urolithiasis, and ureterolithiasis.
What causes kidney stones?
Different kinds of salts in the urine form different kinds of kidney stones:
1) Calcium stones
These are the most common. They are made of calcium and oxalate, which are chemicals found naturally in certain foods (See 'Prevention', below for examples of these foods). A diet with a high content of calcium and oxalate can increase the concentration of these chemicals in the urine and make it more likely for stones to form. Other factors include:
- Vitamin D overdose
- overactive parathyroid glands
- conditions such as cancer, some kidney diseases, or a disease called sarcoidosis
2) Uric acid stones
Excess amounts of uric acid can be caused by eating a lot of meat. Conditions such as gout and treatments such as chemotherapy can also increase the risk of getting uric acid stones.
3) Struvite stones (also called infection stones):
These are caused by having too much ammonia in the urine (a chemical produced by the bacteria that cause urinary tract infections). This kind of stone is most often found in women.
4) Cystine stones
These are caused by a rare hereditary disorder called cystinuria, which affects about 1% of men and women.
Some people are more likely to get kidney stones than others. Men are more prone than women, and people who have had one kidney stone have a 60% chance of getting another stone within 7 years. Other factors include:
- a family history of kidney stones
- being between 20 and 40 years old
- take certain medicines such as diuretics (water tablets), antacids and thyroid medications
- having only one kidney
- eating a diet high in protein but very low in fibre
- not drinking enough fluids
- getting dehydrated through living or working in a hot place
- having poor mobility (eg confined to bed)
The symptoms of kidney stones
Many kidney stones don't move and are too small to cause symptoms. These are often referred to as "silent" stones.
If a kidney stone causes a blockage, or moves down the ureter, it can cause some of the following symptoms:
- pain or aching in the back or one or both sides
- spasms of intense pain (anywhere between the bottom of the ribs and the groin)
- bloody, cloudy or smelly urine
- nausea and vomiting
- frequent urge to urinate
- a burning sensation during urination
- fever and chills
These can also be symptoms of a urinary tract infection, such as cystitis, which is much more common in young women than kidney stone. If you have one or more of these symptoms, see your doctor.
How kidney stones are diagnosed
Doctors can usually diagnose a kidney stone by asking about the symptoms and doing a physical examination. Further tests may be done to confirm the diagnosis, reveal the size and location of the stone, and identify the type of stone. These include:
- Blood tests: to identify excess amounts of certain chemicals related to the formation of stones
- Urine analysis: patients may be asked to collect urine over 24 hours to see if there is a high concentration of the chemicals that cause stones
- X-rays: calcium stones show up white on the X-ray
- Intravenous pyelography (IVP): an X-ray involving an injection of special dye to show up stones that can't be seen with X-rays alone
- Ultrasound: uses high frequency sound waves to produce an image of the internal organs
How kidney stones are treated
Treatment depends on the type and cause of the stone. Most stones can be treated without surgery. Drinking a lot of water (2.5 to 3 litres per day) and staying physically active are often enough to move a stone out of the body.
However, if there is infection or blockage, or a risk of kidney damage, a stone should always be removed. Any infection is treated with antibiotics first. Stones that are too large to pass can be removed in several ways:
Extracorporeal shock wave lithotripsy (ESWL)
This is the most common method and does not involve a surgical operation. Instead, shock waves are used to break the stones into crystals small enough to be passed in the urine. The shock waves do not hurt, although some people feel some discomfort afterwards.
Ureteroscopic stone removal
If a stone is lodged in the ureter, a flexible narrow instrument called a cystoscope can be passed up through the urethra and bladder. The stone is "caught" and removed, or shattered into tiny pieces with a shock wave. This procedure usually involves a general anaesthetic.
If ESWL doesn't work or a stone is particularly large, it may be surgically removed under general anaesthetic. The surgeon makes a small cut in the back and uses a telescopic instrument called a nephroscope to pull the stone out or break it up with shock waves.
Kidney stones caused by chemical imbalance resulting from over-activity of the parathyroid glands (in the neck), is often due to a small benign tumour that can be surgically removed.
What can be done to prevent kidney stones?
Knowing the exact cause and kind of stone enables people to make changes that can help prevent further stones.
- To help prevent any type of stone, fluid intake should be 2.5 to 3 litres per day. Water is best.
- People who get calcium stones should cut down on foods that have high levels of oxalates (meat, chicken, fish, asparagus, nuts and berries, chocolate, cooked spinach, rhubarb, tea and coffee). However, not everyone will benefit from cutting down their calcium intake. It's important to first discuss any dietary changes with a doctor.
- Those who get uric acid stones should eat less meat, fish and poultry. Preventative medicine may be also be prescribed to control the level of acid in the urine.
- People who get "infection" stones need to keep the urine free of bacteria that can cause infection. This may involve taking long-term antibiotics.
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
National Kidney Federation (UK)
National Institute of Diabetes and Digestive and Kidney Diseases