What is Kidney stones?

Kidney stones

What are kidney stones?

Kidney stones are solid, stonelike lumps that can form in your kidneys. Small stones can stay in your kidney without any problems. Small stones may also pass out of your body in your urine without you noticing. But larger stones can block the flow of urine from your kidney. Or they can pass out of your kidney into the tubes that carry urine toward your bladder. This can be very painful.

Your kidneys are two organs that are each about the size of your fist. They sit near the middle of your back, just below your rib cage. Their job is to filter waste products and extra water out of your blood. They send these waste products to your

bladder
Your bladder is the hollow organ at the top of your pelvis that stores urine. It is similar to a balloon, only with stronger walls. It fills up with urine until you go to the bathroom.

bladder as urine.

Source:
National Kidney and Urologic Diseases Information Clearinghouse.
What I need to know about kidney stones.
April 2007. Available at http://www.kidney.niddk.nih.gov/kudiseases/pubs/stones_ez/index.htm (accessed 5 May 2009).

A kidney stone is a lump of crystals made from waste chemicals in your urine. Urine contains chemicals to stop these crystals from forming, but this doesn't always work. Crystals can then clump together and form stones in your kidneys.

Source:
National Institute of Diabetes and Digestive and Kidney Diseases.
Kidney stones in adults.
October 2007. Available at http://kidney.niddk.nih.gov/kudiseases/pubs/stonesadults (accessed on 5 May 2009).

Kidney stones don't just affect your kidneys. You can also get them in other parts of your body that carry urine. The parts of your body that deal with urine are called your urinary tract.

Your urinary tract includes your bladder and ureters. The bladder is the pouch where urine is stored before you urinate. Ureters are tubes that carry urine from the kidneys to the bladder.

You might hear "kidney stone" used as a general term, to mean a stone anywhere in your urinary tract. Doctors sometimes use the terms nephrolithiasis or urolithiasis to describe kidney stones.

Kidney stones come in many shapes and sizes. They can be as small as a grain of sand or as large as a golf ball. They can be smooth or jagged. They are usually yellow or brown.

Kidney stones can be smooth or jagged.

Small stones can stay in your kidneys without causing problems. They can also travel out of your body in the flow of urine. If they are very small, they can pass out of your body without you noticing. But larger ones can block the flow of urine from your kidney. If they pass out of your kidneys, larger stones can rub against the tubes or even get stuck. This can be extremely painful.

About two-thirds of all kidney stones go unnoticed. The rest cause pain on their way out of the body.

Source:
Glowacki LS, Beecroft ML, Cook RJ, et al.
The natural history of asymptomatic urolithiasis.
Journal of Urology. 1992; 147: 319-321.

What causes kidney stones?

Kidney stones form for three main reasons:

Source:
Urology Channel.
Kidney stones.
Available at http://www.urologychannel.com/kidneystones/index.shtml (accessed on 7 May 2009).

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You have a lot of waste chemicals in your urine
You don't have enough citrate in your urine. This is the main chemical that prevents crystals from forming
Your urine doesn't contain enough water to dissolve waste products.

Some things make you more likely to get stones. These are called risk factors. They include:

Source:
Parmar MS.
Kidney stones.
BMJ. 2004; 328: 1420-1424.

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A family history of kidney stones. If a close relative has had kidney stones, you are three times more likely to get them
Having had a kidney stone before. If you've had a kidney stone, you have about a 1 in 2 chance of getting another one in the next few years
High blood pressure. If you have

high blood pressure
Your blood pressure is considered to be high when it is above the accepted normal range. The usual limit for normal blood pressure is 140/90. If either the first (systolic) number is above 140 or the lower (diastolic) number is above 90, a person is considered to have high blood pressure. Doctors sometimes call high blood pressure "hypertension."

high blood pressure, your kidneys have to work harder. This can increase your risk of kidney stones
Gout.

gout
This is a disease of the joints that is caused by a buildup of a chemical called uric acid. This chemical actually forms a crystal within the blood that gets stuck in the joints, causing swelling and pain. Gout attacks often occur in the big toe, but the disease can affect other joints in the body as well. Attacks are excruciatingly painful, but, fortunately, can be treated with a variety of medicines and a special diet.

Gout is a medical condition where you have too much uric acid in your body. Uric acid is a chemical that is usually filtered out by the kidneys. Too much of it can make you more likely to get kidney stones
Overactive parathyroid glands. If your body gets too much of the

hormones
Hormones are chemicals that are made in certain parts of the body. They travel through the bloodstream and have an effect on other parts of the body. For example, the female sex hormone estrogen is made in a woman's ovaries. Estrogen has many different effects on a woman's body. It makes the breasts grow at puberty and helps control periods. It is also needed to get pregnant.

hormone made by the parathyroid glands, extra calcium is released into your blood. This can make you more likely to get kidney stones
Having both ovaries removed, bringing on an early

menopause
When a woman stops having periods, it is called menopause. This usually happens around the age of 50.

menopause
Taking certain medicines, including some

diuretics
Diuretics are a type of medicine that reduce the amount of fluid in your body. The extra fluid is removed in your urine.

diuretics (water pills) and some decongestants
Problems inside your kidney, like cysts.

Types of kidney stones

There are four types of kidney stones.

Calcium oxalate stones (the most common type). These are usually caused by having too much calcium in your body. Calcium that is not needed elsewhere in your body goes to your kidneys as waste. Usually, unwanted calcium is flushed out in your urine. But calcium can build up in the urine. It can then join with other waste products to form a stone.
Uric acid stones. Uric acid is a waste product produced after food is digested. If you have too much uric acid in your urine, it may not dissolve properly. It can then form stones. These kinds of stones are more common in men.
Struvite stones. These stones develop when a urinary infection, such as a bladder infection (

cystitis
Cystitis is an inflammation of the wall of your bladder. It can make you feel as if you want to urinate all the time. The term is often used to describe a urinary tract infection that involves your lower urinary tract (your bladder and urethra) but not your kidneys. These infections are most often caused by bacteria.

cystitis), affects the balance of chemicals in the urine. They are rare, but they happen more often in women, because women have more urinary infections.
Cystine stones. These are quite rare. They are made up of cystine, one of the building blocks of

proteins
A lot of your body's tissues are made out of proteins. Proteins can be made in your cells. Proteins are also part of the food you eat, particularly meat and dairy products. Your body breaks down the protein you eat into amino acids. Your cells then use these amino acids to build new proteins, which make up muscles, joints, hair and other parts of your body.

protein. Cystine does not dissolve well in urine. The stones are caused by a rare inherited condition called cystinuria.

It is important to know what kind of stone you have as this will affect your treatment to prevent future stones. For example, a medicine that helps prevent calcium stones will not work if you have a struvite stone. And the changes in diet that can help prevent uric acid stones may have no effect on calcium stones.

Sources for the information on this page:

National Kidney and Urologic Diseases Information Clearinghouse.What I need to know about kidney stones.April 2007. Available at http://www.kidney.niddk.nih.gov/kudiseases/pubs/stones_ez/index.htm (accessed 5 May 2009).

National Institute of Diabetes and Digestive and Kidney Diseases.Kidney stones in adults.October 2007. Available at http://kidney.niddk.nih.gov/kudiseases/pubs/stonesadults (accessed on 5 May 2009).

Glowacki LS, Beecroft ML, Cook RJ, et al.The natural history of asymptomatic urolithiasis.Journal of Urology. 1992; 147: 319-321.

Urology Channel.Kidney stones.Available at http://www.urologychannel.com/kidneystones/index.shtml (accessed on 7 May 2009).

Parmar MS.Kidney stones.BMJ. 2004; 328: 1420-1424.

This information was last updated on May 08, 2009

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