Kidney Stones FAQ

What are kidney stones?

Urolithiasis is the medical term used to describe stones occurring in the urinary tract. Other frequently used terms are urinary tract stone disease and nephrolithiasis. Doctors also use terms that describe the location of the stone in the urinary tract. For example, a ureteral stone (or ureterolithiasis) is a kidney stone found in the ureter. To keep things simple, we use the term "kidney stones" on this Web site.

Kidney stones are one of the most painful disorders to afflict humans and are also one of the most common disorders of the urinary tract.

Most kidney stones pass out of the body without any intervention by a physician. Cases that cause lasting symptoms or other complications may be treated by various techniques, most of which do not involve major surgery. Research advances also have led to a better understanding of the many factors that promote stone formation.

Who is at risk for kidney stones?

It is estimated that 10 percent of all people in the United States will have kidney stones at some point in their lives. Men tend to be affected more frequently than women. For some unknown reason, the number of persons in the United States with kidney stones has been increasing over the past 20 years. Caucasians are more prone to kidney stones than people of African-American descent. Although stones occur more frequently in men, the number of women who get kidney stones has been increasing over the past 10 years. Kidney stones strike most people between the ages of 20 and 40. Once a person gets more than one stone, he or she is more likely to develop others.

What causes kidney stones?

A kidney stone develops from crystals that separate from urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent or inhibit the crystals from forming. These inhibitors do not seem to work for everyone, however, and some people form stones. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without even being noticed.

Kidney stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate. These chemicals are part of a person's normal diet and make up important parts of the body, such as bones and muscles. A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone. Much less common are the uric acid stone and the rare cystine stone.

We do not always know what causes stones to form. While certain foods may promote stone formation in people who are susceptible, scientists do not believe that eating any specific food causes stones to form in people who are not susceptible.

Absorptive hypercalciuria occurs when the body absorbs too much calcium from food and empties the extra calcium into the urine. This high level of calcium in the urine causes crystals of calcium oxalate or calcium phosphate to form in the kidneys or urinary tract.

Other causes of kidney stones are hyperuricosuria (a disorder of uric acid metabolism), gout, excess intake of vitamin D, and blockage of the urinary tact. Certain diuretics (water pills) or calcium-based antacids may increase the risk of forming kidney stones by increasing the amount of calcium in the urine.

Calcium oxalate stones may also form in people who have a chronic inflammation of the bowel or who have had an intestinal bypass operation or ostomy surgery. Struvite stones can form in people who have had a urinary tract infection.

A person with a family history of kidney stones may be more likely to develop stones. Urinary tract infections, kidney disorders (e.g., cystic kidney diseases) and metabolic disorders (e.g., hyperparathyroidism) are also linked to stone formation. In addition, more than 70 percent of patients with the hereditary disease renal tubular acidosis develop kidney stones.

Cystinuria and hyuperoxaluria are two other rare inherited metabolic disorders that often cause kidney stones. In cystinuria, the kidneys produce too much of the amino acid cystine. Cystine does not dissolve in urine and can build up to form stones. With hyperoxaluria, the body produces too much of the salt oxalate. When there is more oxalate than can be dissolved in the urine, the crystals settle out and form stones.

What are the symptoms?

Usually, the first symptom of a kidney stone is extreme pain. The pain often begins suddenly when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain of the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur with this pain. Later, the pain may spread to the groin.

If the stone is too large to pass easily, the pain continues as the muscles in the wall of the tiny ureter try to squeeze the stone along into the bladder. As a stone grows or moves, blood may be found in the urine. As the stone moves down the ureter closer to the bladder, a person may feel the need to urinate more often or feel a burning sensation during urination. If fever and chills accompany any of these symptoms, an infection may be present. In this case, our office should be contacted immediately.

How are kidney stones diagnosed?

More often, kidney stones are found on an X-ray or sonogram taken on someone who complains of blood in the urine or sudden pain. These diagnostic images give us valuable information about the stone's size and location. Blood and urine tests help detect any abnormal substance that might promote stone formation. Sometimes "silent" stones -- those that do not cause symptoms -- are found on X-rays taken during a general health exam. These stones would likely pass unnoticed.

How are kidney stones treated?

Fortunately, most stones can be treated without surgery. Most kidney stones can pass through the urinary system when the person drinks plenty of water (two to three quarts a day) to help move the stone along. In most cases, a person can stay home during this process, taking pain medicine as needed. You are usually asked to save the passed stone(s) for testing. For surgical alternatives, see our kidney stone prevention and treatment FAQ.