Kidney stones (Renal Lithiasis) are small, hard deposits of mineral and acid salts on the inner surfaces of your kidneys. Normally, the substances that make up kidney stones are diluted in the urine. When urine is concentrated, though, minerals may crystallize, stick together and solidify. The result is a kidney stone. Most kidney stones contain calcium.
Passing kidney stones can be excruciating. The pain they cause typically starts in your side or back, just below your ribs and radiates to your lower abdomen and groin. Painful as they are, kidney stones usually cause no permanent damage. Medical intervention - apart from pain medication - is often unnecessary.
Still, it's important to find out what type of kidney stone you have and why it developed. Some of the underlying causes of kidney stones can be treated to prevent new stones from forming. If no specific treatment exists, you may be able to stave off additional kidney stones simply by drinking more water and making a few dietary changes.
Until a kidney stone moves into the ureter - the tube connecting the kidney and bladder - you may not know you have it. At that point, these signs and symptoms may occur:
Kidney stones that don't cause these symptoms may show up on X-rays when you seek medical care for other problems, such as blood in your urine or recurring urinary tract infections.
Your kidneys are two bean-shaped organs, each about the size of your fist. They're located in back of your abdomen on each side of your spine, and their main function is to remove excess fluid, unneeded electrolytes and wastes from your blood in the form of urine. The ureters carry urine from your kidneys to your bladder, where it's stored until you eliminate it from your body.
Kidney stones form when the components of urine - fluid and various minerals and acids - are out of balance. When this happens, your urine contains more crystal-forming substances, such as calcium and uric acid, than the available fluid can dilute. At the same time, your urine may be short of substances that keep crystals from sticking together and becoming stones. Kidney stones are also prone to develop in highly acidic or highly alkaline urine.
Problems in the way your system absorbs and eliminates calcium and other substances create the conditions for kidney stones to form. Sometimes, the underlying cause is an inherited metabolic disorder or kidney disease. Gout promotes specific types of kidney stones, as does inflammatory bowel disease. So do some drugs, including furosemide (Lasix), used in treating heart failure and high blood pressure, topiramate (Topamax), an anti-seizure drug and indinavir (Crixivan), which is used to treat human immunodeficiency virus, the cause of AIDS.
It's common, however, for kidney stones to have no definite, single cause. A number of factors, often in combination, create the conditions in which susceptible people develop kidney stones. Most kidney stones contain crystals of more than one type. Determining the type that makes up the bulk of the stone - usually a combination of calcium compounds - helps identify the underlying cause. The best preventive approach after your first kidney stone also depends partly on the stone's composition.
Calcium Stones: Roughly four out of five kidney stones are calcium stones, usually in the form of calcium oxalate. Oxalate is found in some fruits and vegetables, but the liver produces most of the body's oxalate supply. Dietary factors, high doses of vitamin D, intestinal bypass surgery and several different metabolic disorders can increase the concentration of calcium or oxalate in urine.
Struvite Stones: Found more often in women, struvite stones are almost always the result of urinary tract infections. Struvite stones may be large enough to fill most of a kidney's urine-collecting space, forming a characteristic stag's-horn shape.
Uric Acid Stones: These stones are formed of uric acid, a byproduct of protein metabolism. You're more likely to develop uric acid stones if you eat a high-protein diet. Gout also leads to uric acid stones. Certain genetic factors and disorders of the blood-producing tissues also may predispose you to the condition.
These factors may increase your risk of developing kidney stones:
Many kidney stones go unnoticed until they cause acute symptoms - specifically, the pain of a stone going through your ureter. Sometimes, however, kidney stones are discovered in the course of looking for the cause of chronic urinary tract infections or blood in the urine.
If your doctor suspects you have kidney stones, you're likely to have a blood analysis to look for excess calcium or uric acid and a 24-hour collection of urine to check whether you're excreting too many stone-forming minerals or too few inhibiting substances.
You may also have one or more of the following imaging tests:
If a stone stays inside one of your kidneys, it usually doesn't cause a problem unless it becomes so large it blocks the flow of urine. This can cause pressure and pain, along with the risk of kidney damage, bleeding and infection. Smaller stones may partially block the thin tubes that connect each kidney to your bladder or the outlet from the bladder itself. These stones may cause ongoing urinary tract infections or kidney damage if left untreated.
Treatment for kidney stones varies, depending on the type of stone and the cause. You may be able to move a stone through your urinary tract simply by drinking plenty of water - as much as 2 to 3 quarts (1.9 to 2.8 liters) a day - and by staying physically active.
Stones that can't be treated with more-conservative measures - either because they're too large to pass on their own or because they cause bleeding, kidney damage or ongoing urinary tract infections - may need professional treatment. Procedures include:
In many cases, you can prevent kidney stones by making a few lifestyle changes. If these measures aren't effective and blood and urine tests reveal a correctable chemical imbalance or that the stones you have are getting bigger, your doctor may prescribe certain medications.
For people with a history of kidney stones, doctors usually recommend passing at least 2.5 quarts (2.3 liters) of urine a day. To do this, you'll need to drink about 14 cups (3.3 liters) of fluids every day - and even more if you live in a hot, dry climate.
What should you drink? Water is best. Include a glass of lemonade every day, too. Make your own with real lemons or use a liquid or frozen concentrate, but avoid powdered lemonade mixes. Lemonade increases the levels of citrate in your urine and citrate helps prevent stone formation.
In addition, if you tend to form calcium oxalate stones, your doctor may recommend restricting foods rich in oxalates. These include rhubarb, star fruit, beets, beet greens, collards, okra, refried beans, spinach, swiss chard, sweet potatoes, sesame seeds, almonds and soy products. What's more, studies show that an overall diet low in salt and very low in animal protein can greatly reduce your chance of developing kidney stones.
As a general rule, restricting your intake of calcium doesn't seem to lower your risk. In fact, researchers have found that women with a high calcium intake are less likely to develop kidney stones than are women who consume less calcium. Why? Dietary calcium binds with oxalates in the gastrointestinal tract so that oxalates can't be absorbed from the intestine and excreted by the kidney to form stones.
An exception to this rule occurs when an individual absorbs too much dietary calcium from the intestine. In such a circumstance, restricting calcium intake is useful.
Calcium supplements seem to have the same protective effect as dietary calcium, but only if they're taken with meals.
Medications can control the level of acidity or alkalinity in your urine and may be helpful in people who form certain kinds of stones. The type of medication your doctor prescribes will depend on the kind of kidney stones you have: