What are Kidney Stones?

Kidney stones are solid, stone-like lumps that form within the kidneys. They can be as small as a grain of sand or as large as the size of a golf ball (sometimes even larger). Most stones are less than a third of an inch in diameter.

The stones are actually accumulations of mineral salts and other substances. Similar stones also can form in most other portions of the urinary tract.

Many of these stones are small enough to pass out of the body during urination, but some larger stones may partially or fully block the normal flow of urine. Kidney stones can cause intense pain and other symptoms.

About 10 percent of people will experience a kidney stone at some time during life. Kidney stones are a common cause of blockage of the urinary tract in adults, accounting for 1 of every 1,000 hospitalizations.

What Are Kidney Stones Made Of?

Kidney stones consist of:

  • A center that consists of crystal-like substances
  • A surrounding region that is composed of layers

Kidney stones are composed of different chemical substances. Each of the major types is named for its main chemical ingredient. They are:

  • Calcium stones
  • Uric acid stones
  • Cystine stones
  • Struvite stones

Are all kidney stones alike?

No. Doctors have found four major types of kidney stones.

1.     The most common type of stone contains calcium. Calcium is a normal part of a healthy diet.

a.     Calcium that is not used by the bones and muscles goes to the kidneys. In most people, the kidneys flush out the extra calcium with the rest of the urine. People who have calcium stones keep the calcium in their kidneys.

b.    The calcium that stays behind joins with other waste products to form a stone. The most common combination is called calcium oxalate.

2.     A struvite stone may form after an infection in the urinary system. These stones contain the mineral magnesium and the waste product ammonia.

3.     A uric acid stone may form when the urine contains too much acid. If you tend to form uric acid stones, you may need to cut back on the amount of meat you eat.

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

When should I consult a doctor?

If you have a kidney stone, you may already know how painful it can be. Most kidney stones pass out of the body without help from a doctor. But sometimes a stone will not pass. It may even get larger. Your doctor can help.

You should consult a doctor if you have any of the following signs:

  • extreme pain in your back or side that will not go away
  • blood in your urine
  • fever and chills
  • vomiting
  • urine that smells bad or looks cloudy
  • a burning feeling when you urinate

These may be signs of a kidney stone that needs a doctor's care.

How will my doctor find out about the kind of stone I have?

The best way for your doctor to find out about the kind of stone you have is to test the stone itself. If you know that you are passing a stone, try to urine through a strainer.

Your doctor may ask for a urine sample or take blood to find out what caused your stone. You may need to collect your urine for a 24-hour period. These tests will help your doctor find ways for you to avoid stones in the future.

Why do I need to know the kind of stone?

The therapy your doctor gives you depends on the type of stone you have. For example, a medicine that helps prevent calcium stones will not work if you have a struvite stone. The diet changes that help prevent uric acid stones may not work to prevent calcium stones. Therefore, careful analysis of the stone will help to guide your treatment.

What can I do to avoid more stones?

  1. Drink more water. Try to drink 12 full glasses of water a day. Drinking lots of water helps to flush away the substances that form stones in the kidneys.
  2. You can also drink ginger ale, lemon/lime sodas, and fruit juices. But water is best. Limit your coffee, tea, and cola to 1 or 2 cups a day because the caffeine may cause you to lose fluid too quickly.
  3. Your doctor may ask you to eat more of some foods and to cut back on other foods. For example, if you have a uric acid stone, your doctor may ask you to eat less meat, because meat breaks down to make uric acid.
  4. If you are prone to forming calcium oxalate stones, you may need to limit foods that are high in oxalate. These foods include rhubarb, beets, spinach, and chocolate.
  5. The doctor may give you medicines to prevent calcium and uric acid stones.

If you suspect that you are suffering from a kidney stone, go to your nearest clinic or day hospital for a medical examination.

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Page updated: 17 August 2011