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What are kidney stones?
A kidney stone normally begins as a small crystal-like material and it gradually builds up into a larger, solid mass. Urine normally contains chemicals that inhibit the crystals from forming. Or, if crystals remain small enough they can travel through the urinary tract and pass out of the body without being noticed. However, when crystals combine together to form a kidney stone, it can stick to the lining of the kidney or settle in an area where urine cannot carry it out of the body.
What causes kidney stones?
More than 90% of individuals with kidney stones have a chemical abnormality of blood or urine that contributes to the tendency to form the stones. In all people, not drinking enough water or other fluids may also contribute to forming stones. Inadequate fluid intake causes the kidneys to produce less urine, as well as urine that is highly concentrated. The smaller the daily volume of urine, the more likely it is that a person would form kidney stones.
Certain people are more likely to develop stones. A variety of factors increase a person’s likelihood for kidney stones, including:
- Age - more common during middle age
- Activity level - more common in people who are immobilized or after excessive fluid loss through sweating
- Climate - more common in hot climates or during the summer months
- A family history of kidney stones
What chemical abnormalities are known to cause kidney stones?
The chemical abnormalities relate to the type of stones that form in the kidneys. These four types of stones and the chemical abnormalities that cause them are:
- Calcium Stones: people who form this type of stone either have too much of one type of three chemicals in their urine, or not enough of another. In particular, they have either too much calcium, oxalate, or urate in their urine, or too little citrate. Eating too much salt may cause too much calcium to stay in the urine A few patients will have kidney stones from overproduction of the calcium controlling hormone, parathormone. Drinking milk does not cause kidney stones.
- Struvite Stones: Chronic infection of the urine generally causes these stones. The bacteria responsible for the infection cause a chemical alteration of urine which leads to this type of stone.
- Uric Acid Stones: This type of stone forms when the urine is too acidic, which causes excessive uric acid production.
- Cystine Stones: These stones form because of an inherited condition in which the body cannot clear a chemical called cystine from the blood. Usually, other family members have the same condition.
Knowing the type of kidney stone is important to prescribing treatment to prevent other stones from forming.
How are kidney stones diagnosed?
If a person is suspected of having kidney stones, either because of pain or blood in the urine, the physician may order x-rays or an ultrasound examination of the kidneys, ureters (tubes that carry urine from the kidneys to the bladder) and the bladder. If present, most kidney stones can be seen on an x-ray, although sometimes an ultrasound examination is necessary to see other types of kidney stones.
Several tests are used to look for kidney stones, including plain abdominal X-ray, ultrasound, intravenous pyelography, or CT scan.
You might receive an injection of dye before the X-ray is taken. The dye is used to get a better image of the size and location of the kidney stone. (This type of X-ray is often called IVP or intravenous pyelography.)
This test looks for very small kidney stones in the urine. The urine is strained. Any stones found in the urine are analyzed to determine their chemical composition.
Patients are questioned about their diet, use of medicine, lifestyle, and family's medical history.
How Kidney Stones Leave the Body
In many cases, a person will pass the stone via the urine. This may be a painful process, and may take a couple of days. Generally, the physician asks the person with kidney stones diagnosed by x-ray or ultrasound to strain the urine and save the stone so that it can be analyzed.
When a person cannot pass the stone through the urine, there are treatments available to remove or crush them, including:
- Inserting a small instrument through the urethra (the tube through which a person passes urine from the body) to “snare” the stone and remove it
- Shock wave lithotripsy, whereby the stone is crushed. Once the stone is crushed, a person can pass the smaller pieces
What are the symptoms of kidney stones?
Sometimes kidney stones cause no symptoms. When kidney stones are large or there is more than one, they may block the flow of urine. The most common symptoms of kidney stones are blood in the urine or pain. Pain severity and location of pain might vary depending on such factors as stone location and degree of obstruction. Other symptoms include:
- Feeling the need to urinate often
- Inability to urinate (when a stone blocks the urinary tract)
Cloudy, foul smelling urine, fever, chills, or weakness might be a sign of a serious infection. If you experience these symptoms, please contact a Cleveland Clinic urologist as soon as possible.
How are kidney stones treated?
The Cleveland Clinic Kidney Stone Center offers patients extracorporeal shock wave lithotripsy as a treatment option for kidney stones. Shock wave lithotripsy is a noninvasive technology that uses shock waves to disintegrate kidney stones. The stones are broken into small particles which can then pass on their own.
During shock wave lithotripsy, a specialized table allows urologists to localize the stone, and to simultaneously focus shock waves on it. The procedure takes approximately one hour and patients are generally discharged from the hospital a few hours after the treatment.
Most kidney stone patients are eligible for SWL, although some are not suitable candidates. Factors such as size, location and number of stones, height, weight, pregnancy and heart problems may indicate the need for a different treatment such as laser or ultrasound.
Cleveland Clinic physicians also offer the ureteroscopy procedure to treat kidney stones. In a ureteroscopy a flexible camera is inserted into the bladder and ureter to find and remove the kidney stone. Many patients find this a preferable option as it is done on an outpatient basis.
Another potential option is Percutaneous nephrolithotomy (PCNL). Percutaneous nephrolithotomy is a surgical treatment for larger kidney stones (typically over 2cm in diameter). This minimally invasive surgery is an effective way to remove larger kidney stones that are too difficult to treat with other methods.
Can I prevent kidney stones?
Research has shown that a variety of diet-related factors may contribute to the formation of kidney stones. The foods and beverages you eat and drink can help prevent new stones. If your doctor detects high levels of urinary oxalate, they may recommend a oxalate controlled diet for kidney stones to patients who frequently suffer from the condition.
Drinking enough liquids each day helps to keep your urine “diluted”. This greatly reduces the chances of forming kidney stones. Drink 8 to 10 cups of liquids each day. At least half of the liquid you drink should be water. The other liquids could be any beverages you like - juice, milk, coffee, or flavored beverages. Drink alcohol only in moderation or not at all.
Important: Drink at least one cup of liquid at bedtime.
Reduce, or keep to a minimum, the amount of salt that you eat:
- Avoid using salt at the table
- Reduce or don’t use salt in cooking
- Reduce or don’t use high sodium foods such as processed meats (ham, hot dogs, sausage, luncheon meat) or convenience foods (regular, canned or boxed soups, noodle or rice mixes)
- Choose unsalted pretzels, crackers and popcorn instead of salty snacks
Fat and Fiber
Follow a low fat, high fiber lifestyle:
- Limit daily amount of meat, fish and poultry to five ounces (cooked weight, without bone)
- Instead of frying foods, bake, broil, roast, boil, steam or stir-fry (in a small amount of no-fat liquid such as water or pineapple juice)
- Cut back on the amount of butter, margarine, oil, sour cream and salad dressings that you use. Choose low fat or no-fat alternatives
- Include a variety of high fiber foods at each meal. Choose from whole grain breads, cereals and pastas as well as fruits and allowed vegetables
Low Fat Dairy Products
In the past, avoiding dairy products was suggested to prevent kidney stones. This is no longer done. Current research shows that eating a moderate amount of high calcium foods with meals (at least two servings each day) may actually decrease the chances of forming stones.
Important: Remember to choose low fat dairy products or calcium fortified beverages.
Foods to Avoid
The following foods are high in oxalate or cause an increase in uric acid in your urine which may also increase the formation of kidney stones: Chocolate, rhubarb, greens (spinach, collard, beet and turnip greens), berries, peanuts, asparagus, tea, anchovies, caviar, herring, scallops, mussels, organ meats (liver, kidneys, brains), meat extracts (broth, bouillon, consomme, gravy)
Working with your physician to help prevent kidney stones in the future is a very helpful strategy. Once your Cleveland Clinic physician diagnoses you, you may be prescribed certain medications to help prevent future stones. These medications include:
- Hydrochlorothiazide, a diuretic which is very effective in reducing calcium in the urine and preventing kidney stones
- Potassium citrate taken orally makes the urine less acidic and more alkaline. In turn, this decreases the amount of uric acid and cystine in the urine
- Tiopronin and/or captopril: These two drugs have been found useful in reducing the excretion of cystine in patients who have this as the cause for their kidney stones
- Antibiotics: In those patients who have struvite (infection) stones, preventing or controlling urinary infection is mandatory to prevent the recurrence of stones
- Allopurinol reduces the amount of uric acid excretion