Kidney stones are hard deposits that form when certain minerals and salts become highly concentrated in urine. They can cause severe pain when they move into the urinary tract, but small stones may pass without invasive treatment.
The main types include calcium stones, uric acid stones, struvite stones and cystine stones. Treatment and prevention depend largely on what the stone is made of, as well as its size and location.
What causes kidney stones?
Kidney stones form when urine contains high levels of substances such as calcium, oxalate and phosphorus. When there is not enough fluid to keep these substances diluted, crystals can form and gradually develop into stones.
A number of factors can increase the risk, including not drinking enough fluids, obesity, a family history of kidney stones, certain digestive conditions and recurrent urinary tract infections. Some medicines can also increase the risk in certain people.
Struvite stones are different because they are associated with urinary tract infections. The other major types, including calcium, uric acid and cystine stones, have different causes and risk factors.
Symptoms of kidney stones
Kidney stones may cause no symptoms while they remain in the kidney. Symptoms often begin when a stone moves into a ureter, the narrow tube connecting the kidney to the bladder.
Common symptoms include sharp pain in the back, side, lower abdomen or groin. The pain can come in waves and may change location as the stone moves.
Other symptoms include pain or burning during urination, frequent or urgent urination, blood in the urine, nausea and vomiting. Urine may also become cloudy or have a bad smell. Fever and chills can occur when an infection is present.
People with severe pain, fever or chills, blood in the urine, persistent vomiting or difficulty passing urine should seek medical attention promptly. A blocked urinary tract combined with an infection can require urgent treatment.
How kidney stones are treated
Treatment depends on the size and location of the stone, its composition and the severity of symptoms.
Small stones may pass through the urinary tract without a procedure. A health professional may recommend drinking enough fluids and may prescribe pain medicine. Some patients may also be given medication to help a stone pass.
Larger stones, stones that block urine flow or stones causing severe or persistent problems may require a procedure. Depending on the circumstances, doctors may use shock waves to break a stone into smaller pieces or remove it through a minimally invasive procedure.
Drinking water can help small stones pass and is one of the most important measures for preventing future stones. It does not, however, dissolve every type of kidney stone.
Diet and prevention
The most important general measure for preventing kidney stones is drinking enough liquid, mainly water, to keep urine diluted. The amount needed varies depending on a person’s health, activity level and climate. People with certain medical conditions may need specific advice from a health professional about fluid intake.
Dietary changes should be based on the type of stone a person has had.
People who develop calcium oxalate stones may be advised to reduce foods high in oxalate, including spinach, while also limiting excessive sodium. However, avoiding all calcium-containing foods is not generally recommended. Adequate dietary calcium can help reduce the amount of oxalate absorbed by the body.
For uric acid stones, reducing excessive animal protein may help lower the risk of recurrence. People with calcium stones may also be advised to moderate animal protein and sodium intake.
A dietitian or other health professional can help determine which dietary changes are appropriate after the stone has been analysed.
When to seek medical care
Kidney stone symptoms can resemble those of other urinary conditions, so symptoms alone cannot establish the diagnosis.
Medical evaluation may include a physical examination, urine and blood tests and imaging to determine whether a stone is present and whether it is blocking the urinary tract.
People who have severe pain, fever or chills, blood in the urine, persistent vomiting or difficulty urinating should seek medical attention rather than relying on home treatment.
For people who have had kidney stones before, identifying the stone’s type and possible cause can help guide measures to prevent another episode. Those measures may include changes to fluid intake, diet and, in some cases, medication.
