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  Kidney Stones - The Basics
 

What are kidney stones?

Kidney stones are formed by crystallization of natural chemical or substances in the urine. The key event in stone formation is supersaturation. To understand this concept, picture a glass of water containing salt. If there is little salt, it dissolves. As more salt is added, a point is reached at which the concentration of salt is just high enough to prevent the crystals from dissolving. At this point, the solution is said to be saturated. If even more salt is added, crystals will precipitate or form stones.

Beside supersaturation, other factors that may cause stone formation include the presence of infection, obstruction, and foreign body in the urinary tract.

What are the main types of urinary (kidney) stones?

Almost 95% of all kidney stones are calcium stones. High level of calcium in the urine may result from defective kidney function, excessive absorption from the stomach and intestines, inflammatory bowel disease, and abnormal function of the parathyroid gland. Most calcium stones are calcium oxalate stones. Oxalate is present in many foods, and its level in the urine may also be affected by a high salt diet.

Other stone types are much less common. Uric acid stones are common in people who have gout. Struvite stones are associated with infection-causing bacteria in the urinary tract. Cystine stones occur in people with the genetic disease called cystinuria. This type of stone formation is almost always diagnosed during childhood.

When do stones cause symptoms?

Most stones only cause symptoms when they are passing from the kidney pelvis down the small-caliber ureter. The most common symptom is severe back or abdominal pain. This may be accompanied by nausea and vomiting. The presence of fever, chills, and sweats suggest an associated urinary tract infection. Usually blood cells are seen only with a microscope but occasionally it is more obvious.

How common is kidney stones?

It is estimated that the prevalence of kidney stones is about two to three percent. In 1993, kidney stone disease cost the American economy $1.7 billion, including indirect costs from loss of productivity.

Until the 1980's, kidney stones were a major health problem, with a significant proportion of patients requiring extensive surgery and a sizable minority losing a kidney. The advent of extracorporeal shock-wave lithotripsy (ESWL) and the refinement of endoscopic surgery, however, have greatly decreased the morbidity associated with stone surgery, and the disease is changing from a major health problem to a major nuisance.

What are the risk factors for kidney stones?

Genetics: kidney stones are relatively rare in Native Americans, blacks in Africa and America, and native-born Israelis. The incidence of stones is highest in some of the colder temperate areas of the world, populated mainly by Asians and Whites. About 25% of patients with stones have a family history of kidney stones. Although the familial or hereditary theories of stone formation is not completed understood, there is data supporting household diet and familial tendencies in the theories of causes of kidney stones. Known hereditary disorders causing kidney stones include renal tubular acidosis (RTA), and cystinuria.

Age and Sex: The peak incidence of stones is from the twenties to the forties. Male to female ratio is about three to one. Stones associated with urinary tract infections, cystinuria, and hyperparathyroidism are more commonly in women.

Geography: The prevalence of stones is higher in those who live in mountainous, desert, or tropical areas. High-incidence areas include the United States, British Isles, Scandinavian countries, Mediterranean countries, northern India and Pakistan, northern Australia, central Europe, portion of the Malayan peninsula, and China.

Climatic and Seasonal factors: The effect of geography on the prevalence of stone disease may be indirect, through its effect on temperature. Stone formation (especially uric acid stones) is more common during the summer months. Higher temperature increase perspiration, which may result in concentrated urine. This promotes increase stone crystallization.

Diet: Intake of various foods and fluids that result in greater urinary excretion of substances that produce stones has a significant effect on incidence of urinary stones. Data suggests that patients who form stones may have exceptional dietary patterns, especially dietary excesses of particular foods and fluids.

How is it diagnosed?

Your doctor may suspect you have kidney stones based on your symptoms and the presence of blood in your urine. Several imaging tests are available to identify the stone(s) number, size and location in order to plan treatment or management. Commonly used tests are CT scan, Intravenous pyelogram (IVP), and ultrasound.

How is it treated or managed?

In most cases, the initial management is usually pain control. Most patients are able to get relief and managed with oral pain medication. Hospital admission is indicated for poor pain control with oral medication, persistent nausea and vomiting, and infection. The eventual treatment depends on the size and location of the stone(s), and whether there is evidence of infection. Infection can be particularly severe in high-risk patients such as the elderly, and the diabetics.

How long will the initial symptoms last?

The initial acute pain usually lasts hours to 1 to 2 days. A stone, however, may take days or even weeks to pass. X-rays will be necessary during follow-up, since being pain-free may not necessarily mean passage of the stone.

What can be done to help prevent kidney stones?

If there are no clear underlying health problems, the most effective measure may be drinking plenty of water daily. Extra water intake is needed during the summer months and during physical activities to avoid dehydration.
Specific dietary recommendations can be made after review of your dietary habits, stone composition analysis, and study of blood and urine chemistries.

*  This information is not intended to substitute for a consultation with a urologist. It is offered to educate patients on the basis of urological conditions in order to get the most out of their office visits and consultations. Please see our web page disclaimer for addition information.


 

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