- Risk factors
- Tests and diagnosis
- Treatments and drugs
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:
- Pain in the side and back, below the ribs
- Fluctuations in pain intensity, with periods of pain lasting 20 to 60 minutes
- Pain waves radiating from the side and back to the lower abdomen and groin
- Bloody, cloudy or foul-smelling urine
- Pain on urination
- Nausea and vomiting
- Persistent urge to urinate
- Fever and chills if an infection is present
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:
- Lack of fluids: If you don't drink enough fluids, especially water, your urine is likely to have higher concentrations of substances that can form stones. That's also why you're more likely to form kidney stones if you live in a hot, dry climate or exercise strenuously without replacing lost fluids.
- Family or personal history: If someone in your family has kidney stones, you're more likely to develop stones too. And if you've already had one or more kidney stones, you're at increased risk of developing another.
- Age and sex: Most people who develop kidney stones are between 20 and 70 years of age. Men are more likely to develop kidney stones than are women.
- Diet: A high-protein, high-sodium and low-calcium diet may increase your risk of some types of kidney stones.
- Limited activity: You're more prone to develop kidney stones if you're bedridden or very sedentary for a long period of time. That's partly because limited activity can cause your bones to release more calcium.
- Obesity: High body mass index (BMI), increased waist size and weight gain have been linked to kidney stones in long-term studies of large populations. The relationship is strongest in women.
- High blood pressure: Having high blood pressure doubles your risk of forming kidney stones.
- Gastric bypass surgery, inflammatory bowel disease or chronic diarrhea: Changes in the digestive process affect your absorption of calcium and increase the levels of stone-forming substances in your urine.
Tests And Diagnosis
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:
- Computerized tomography (CT) scan: This imaging test has become the standard of care for evaluating acute kidney stones. It's rapidly performed, can identify stones regardless of composition and doesn't require the use of contrast dye.
- Abdominal X-ray: An abdominal X-ray can visualize most kidney stones and can help to judge changes in the size of a stone over time.
- Ultrasound: Instead of X-rays, this diagnostic technique combines high-frequency radio waves and computer processing to view your internal organs. It's safe, painless and noninvasive, but it may miss small stones, especially if they're located in a ureter or your bladder.
- Intravenous pyelography (excretory urogram): This study can be useful in determining the location of stones in the urinary system and can define the degree of blockage caused by a stone. A contrast dye is injected into a vein in your arm and a series of X-rays is taken as the dye moves through your kidneys, ureters and bladder. This study has largely been replaced by the CT scan but is still useful in limited circumstances
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.
Treatments And Drugs
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:
- Extracorporeal shock wave lithotripsy (ESWL): This is a commonly used procedure for treating kidney stones. It uses shock waves to break the stones into tiny pieces that are then passed in your urine. In some cases, you may be partially submerged in a tub of water during the procedure. In others, you may lie on a soft cushion. You'll generally require sedation or light anesthesia due to moderate pain caused by the shock waves. A loud noise is produced each time a shock wave is generated, and you'll wear earphones to protect your hearing.
- Your doctor will likely use X-rays or ultrasound to help determine the position of the stone as well as to monitor the status of the stone during treatment.
- Complications that may occur with ESWL include blood in the urine, bruising on the back or abdomen, bleeding around the kidney and other adjacent organs, and discomfort as the stone fragments pass through the urinary tract. In addition, if the stone doesn't shatter completely, you may need a second round of ESWL or ureteroscopic stone removal. After treatment, it may take months for all the stone fragments to pass.
- Percutaneous nephrolithotomy: When ESWL isn't effective, or the stone is very large, your surgeon may remove your kidney stone through a small incision in your back using an instrument called a nephroscope.
- Ureteroscopic stone removal: This procedure may be used to remove a stone lodged in a ureter. The stone is snared with a small instrument (ureteroscope) that's passed into the ureter through your bladder. Ultrasound or laser energy also can be directed through the scope to shatter the stone. These methods work especially well on stones in the lower part of the ureter.
- Parathyroid surgery: Some calcium stones are caused by overactive parathyroid glands, which are located on the four corners of your thyroid gland, just below your Adam's apple. When these glands produce too much parathyroid hormone, your body's level of calcium can become too high, resulting in excessive excretion of calcium in your urine. Most often, this is the result of a small benign tumor in one of your four parathyroid glands. A doctor can surgically remove the tumor.
Prevention 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:
- Calcium stones: To help prevent calcium stones from forming, your doctor may prescribe a thiazide diuretic or a phosphate-containing preparation. If you have calcium stones because of a condition known as renal tubular acidosis, your doctor may suggest taking sodium bicarbonate or potassium bicarbonate.
- Uric acid stones: Your doctor may prescribe allopurinol (Zyloprim, Aloprim) to reduce uric acid levels in your blood and urine and a medicine to keep your urine alkaline. In some cases, allopurinol and an alkalinizing agent may dissolve the uric acid stones.
- Struvite stones: To prevent struvite stones, the first goal is to keep urine free of bacteria that cause infection. Long-term use of antibiotics in small doses may be useful to achieve this goal.