What is a kidney stone?

A kidney stone is a solid piece of material that forms from crystallization of excreted substances in the urine. The stone may remain in the kidney or break loose and travel down the urinary tract. A small stone may pass all of the way out of the body, but a larger stone can get stuck in a ureter, the bladder, or the urethra. This may block the flow of urine and cause great pain.

A kidney stone may be as small as a grain of sand or as large as a pearl, and some are as big as golf balls. They may be smooth, irregular in shape, or jagged, and are usually yellow or brown in color.

Who is affected by kidney stones?

Kidney stones are one of the most painful disorders, and one of the most common disorders of the urinary tract. The National Institute of Diabetes and Kidney Disease (NIDKD) estimates that about a million people in the United States are treated for kidney stones each year. Consider these NIDKD statistics:

  • Caucasians are more prone to kidney stones than are African-Americans.

  • Although stones occur more frequently in men, the number of women who develop kidney stones has been increasing.

  • Kidney stones strike mostly people between age 20 and 40.

  • Once a person develops more than one stone, he/she is more likely to develop additional stones.

What are some of the different types of 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. However, in some people, stones still form. Crystals that remain small enough will travel through the urinary tract and pass out of the body in the urine without even being noticed.

  • Calcium stones. Calcium stones are the most common type of stones. Calcium is a normal part of a healthy diet and is used by bones and muscles. Calcium not used by the body goes to the kidneys where it is normally flushed out with the rest of the urine. In some people, however, the calcium that stays behind joins with other waste products to form a stone.

  • Struvite stones. Struvite stones are a type of stone that contains the mineral magnesium and the waste product ammonia. It may form after an infection in the urinary system.

  • Uric acid stones. Uric acid stones may form when there is too much acid in the urine.

  • Cystine stones. Cystine, one of the building blocks that make up muscles, nerves, and other parts of the body, can build up in the urine and form a stone. Cystine stones are rare. The disease that causes cystine stones (cystinosis) runs in families.

What are the symptoms of kidney stones?

The following are the most common symptoms of kidney stones. However, each individual may experience symptoms differently. Symptoms may include:

  • Extreme, sharp pain in the back or side that will not go away. Changing positions does not help. Pain can come and go.

  • Blood in the urine

  • Nausea and vomiting

  • Cloudy or odorous urine

  • Frequent urination

  • A burning feeling when you urinate

  • Fever and chills

Prompt medical attention for kidney stones is necessary.

The symptoms of kidney stones may resemble other conditions or medical problems. Always consult your physician for a diagnosis.

How are kidney stones diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures for kidney stones may include the following:

  • Intravenous pyelogram (IVP). A series of X-rays of the kidney, ureters, and bladder with the injection of a contrast dye into the vein—to detect tumors, abnormalities, kidney stones, or any obstructions, and to assess renal blood flow.

  • Computerized tomography (CT) scan. Combines special X-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor or printed.

  • Urinalysis. Laboratory examination of urine for various cells and chemicals, such as red blood cells, white blood cells, infection, or excessive protein.

  • Blood tests. Laboratory examination of the blood to detect substances that might promote stone formation.

  • Renal ultrasound. A non-invasive test in which a transducer is passed over the kidney producing sound waves which bounce off of the kidney, transmitting a picture of the organ on a video screen. The test is used to determine the size and shape of the kidney, and to detect a mass, kidney stone, cyst, or other obstruction in the kidney.



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