Kidney stones

Kidney stones, one of the most painful of the urologic disorders, are not a product of modern life. Scientists have found evidence of kidney stones in a 7,000-year-old Egyptian mummy. Unfortunately, kidney stones are one of the most common disorders of the urinary tract; more than 1 million cases were diagnosed in 1996. An estimated 10 percent of people in the United States will have a kidney stone at some point in their lives. Men tend to be affected more frequently than women.  These have now been attributed, in some cases, to exposure of toxigenic molds.

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

A kidney stone is a hard mass developed from crystals that separate from the urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent the crystals from forming. These inhibitors do not seem to work for everyone, however, so 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 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.

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, however, the term "kidney stones" is used throughout this fact sheet.

Gallstones and kidney stones are not related. They form in different areas of the body. If you have a gallstone, you are not necessarily more likely to develop kidney stones.

For unknown reasons, the number of people in the United States with kidney stones has been increasing over the past 20 years. White Americans are more prone to develop kidney stones than African Americans. Although stones occur more frequently in men, the number of women who get them has been increasing over the past 10 years, causing the ratio to change. Kidney stones strike most typically between the ages of 20 and 40. Once a person gets more than one stone, others are likely to develop.

Doctors do not always know what causes a stone 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.

A person with a family history of kidney stones may be more likely to develop stones. Urinary tract infections, kidney disorders such as cystic kidney diseases, and metabolic disorders such as hyperparathyroidism are also linked to stone formation.

In addition, more than 70 percent of people with a rare hereditary disease called renal tubular acidosis develop kidney stones.

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 tract. 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.

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 in the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur. Later, pain may spread to the groin.

If the stone is too large to pass easily, 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 appear in the urine. As the stone moves down the ureter closer to the bladder, you 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, you should contact a doctor immediately.

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.

Fortunately, surgery is not usually necessary. Most kidney stones can pass through the urinary system with plenty of water (2 to 3 quarts a day) to help move the stone along. Often, you can stay home during this process, drinking fluids and taking pain medication as needed. The doctor usually asks you to save the passed stone  for testing. (You can catch it in a cup or tea strainer used only for this purpose.)

If you've had more than one kidney stone, you are likely to form another; so prevention is very important. To prevent stones from forming, your doctor must determine their cause. Tests are now available to determine fungal exposure as well.  He or she will order laboratory tests, including urine and blood tests. Your doctor will also ask about your medical history, occupation, and eating habits. If a stone has been removed, or if you've passed a stone and saved it, the laboratory can analyze it to determine its composition.

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