A kidney stone is formed when a small speck of mineral settles out of the urine into the kidney or the ureter, a tube that links the kidney to the bladder. Additional minerals will stick to the small speck, which develops into stones over time.
There are four main types of kidney stones, classified depending on the chemicals that make up the stones: calcium salts (calcium oxalate, calcium phosphate, mixed calcium oxalate/phosphate), magnesium ammonium phosphate (struvite), uric acid, or cystine. Though rare, certain medications can sometimes form stones after crystallization in the urine. The most common kidney stones are composed of calcium oxalate, which is naturally present in the urine.
Kidney stones are a common cause for hospital visits in North America. It's estimated that about 10% of North Americans will have a kidney stone at least once during their lifetime, most commonly seen in people aged 20 to 50 years old.
The stones are often small and can pass through the urinary system on their own. Kidney stones are more likely to form in hot climates or in the summertime. When people become dehydrated, the minerals in their urine become more concentrated. It then becomes easier for small mineral particles to settle out of the urine and start a kidney stone. Kidney stones are three times more common in men than in women. They also seem to run in families. People who have already had one kidney stone also have a higher than average risk of getting another.
There is no single cause for kidney stones, however dehydration is a key risk factor. Kidney stones can also be caused by an imbalance in a person's metabolism causing abnormally high levels of mineral salts to collect in the urine. Stones made up of uric acid occur in people who have diseases such as gout, chronic dehydration, and some cancers.
Hyperparathyroidism, a condition in which the parathyroid gland is overactive, can also be linked to kidney stones. Certain disorders of the bowel or intestines can also lead to kidney stones, as can a chronic bacterial infection of the urinary system.
Symptoms and Complications
Small stones in the kidney are often painless. Larger stones can block the flow of urine and cause the kidney to swell painfully. If a stone moves into the ureter, it can cause sudden severe pain called renal colic. Renal colic is described as intermittent and episodic, lasting for several minutes at a time and is most often noticed in the early morning or late into the night, when you are at rest or in a sitting position. Kidney stones can also cause nausea and vomiting, blood in the urine, fever, and pain with urination.
If the urinary flow is blocked, the kidney can be quickly damaged. A severe infection called pyelonephritis can also occur due to blocked urinary flow.
Making the Diagnosis
A doctor will perform a series of blood and urine tests to determine if someone has kidney stones. Imaging tests such as a CT scan or ultrasound, are used in the diagnosis of kidney stones.
If a stone is found, a doctor may order metabolic tests to determine whether a problem with the body's metabolism could be the cause. These may include blood tests and tests of urine samples taken over 24 hours (such as urinalysis, urine pH, and urine culture). If a stone is passed, it will be analyzed to see what it contains.
Treatment and Prevention
The pain caused by kidney stones can be treated with non-prescription and prescription pain medication, bed rest, and drinking lots of fluids to prevent dehydration.
Most stones pass through the system by themselves within six weeks, but some need to either be broken up into smaller pieces or surgically removed. Stones can be broken up using treatment techniques called extracorporeal shock wave lithotripsy, cystoscopy, or percutaneous lithotripsy.
In extracorporeal shock wave lithotripsy, shock waves (high intensity ultrasound) pass through water pouches placed on the skin and are directed towards the stone. They break the stone into small pieces that can pass out through the ureter. You do not need to stay overnight at the hospital to have this procedure.
If the stone is in the bladder or the higher part of the ureter, it can be crushed using cystoscopy. In this procedure, your doctor will pass a viewing tube and a crushing device into the bladder or lower ureter. The crushing device can be used to pull out the stone, or it can break it up with laser or electric energy.
Stones that are too large to be removed as a whole can be broken up using percutaneous lithotripsy. A viewing tube is inserted through an incision in the side of the body. The stone is then broken up with ultrasound or electric energy.
Surgery is only used in cases where the other procedures have not worked. This usually happens when stones are large or hard to reach. Surgery is done under general anesthesia. The doctor makes an incision into the side of the body, and another into the ureter or kidney to remove the stone. The incisions are then stitched up.
If the stone has formed due to problems with the metabolism, your doctor may prescribe a special diet as well as medications to control the problem. For example, taking allopurinol*, a medication that decreases the production of uric acid, helps prevent kidney stones composed of uric acid. This is the same medication that is prescribed for gout. Thiazide diuretics can prevent the formation of kidney stones made of calcium. Some people's bodies lack a chemical called citrate. Citrate supplements may help prevent kidney stones in these people.
Kidney stones can be prevented by drinking 8 to 12 glasses of water every day and by drinking fluids with meals. It is important to drink enough fluids so that urine appears almost colourless. Your doctor may also recommend cutting down on the amount of protein and salt in the diet.