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 summer time. 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 known cause for kidney stones, although 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. In addition, certain disorders of the bowel or intestines can also lead to kidney stones, as can a chronic bacterial infection of the urinary system.
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, 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.