Renal Lithiasis / Kidney Stones
If you've ever passed a kidney stone, you're not likely to forget the experience — it can be excruciatingly painful. Kidney stones (renal lithiasis) are an ancient affliction dating back to the age of the Egyptian pyramids, yet they are still a common disorder today. The incidence of kidney stones has been increasing in recent decades. Although the reasons for this are still unclear, many experts believe that diet choices and lack of fluids are important factors that have contributed to this increase.
Not all kidney stones cause symptoms. They're often discovered when you have X-rays for an unrelated condition or when you seek medical care for other problems, such as blood in your urine or recurring urinary tract infections. The pain becomes agonizing only when a kidney stone breaks loose and begins to work its way down from your kidneys to your bladder through the connecting tube (ureter).
Kidney stones usually form when your urine becomes too concentrated. This causes minerals and other substances in urine to form crystals on the inner surfaces of your kidneys. Over time, these crystals may combine to form a small, hard mass, or stone.
Most small kidney stones pass into your bladder without causing any permanent damage. Still, it's important to determine the underlying cause so that you don't form more stones in the future. In many cases, you can prevent kidney stones simply by drinking more water and making a few dietary changes.
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 waste 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.
The crystals that lead to kidney stones are likely to form when your urine contains a high concentration of certain substances — especially calcium, oxalate, uric acid and rarely, cystine — or low levels of substances that help prevent crystal formation, such as citrate and magnesium. Crystals also may form if your urine becomes too concentrated or is too acidic or too alkaline.
A number of factors can cause changes in your urine, including the effects of heredity, diet, drugs, climate, lifestyle factors and certain medical conditions. Each of the four main types of kidney stones has a different cause :
- Calcium stones. Roughly four out of five kidney stones are calcium stones. These stones are usually a combination of calcium and oxalate. Oxalate is a compound that occurs naturally in some fruits and vegetables. A number of factors can cause high concentrations of these substances in urine. Excess calcium, for instance, may result from ingesting large amounts of vitamin D, from treatment with thyroid hormones or certain diuretics, and from some cancers and kidney conditions. You may also have high levels of calcium if your parathyroid glands, which regulate calcium metabolism, are overactive (hyperparathyroidism). On the other hand, certain genetic factors, intestinal bypass surgery and a diet high in oxalic acid may cause excess amounts of oxalate in your body.
- Struvite stones. Found more often in women than in men, struvite stones are almost always the result of chronic urinary tract infections caused by bacteria that produce specific enzymes. These enzymes increase the amount of ammonia in the urine, which is incorporated in the crystals of struvite stones. These stones are often large, may have a characteristic stag's-horn shape and can seriously damage your kidneys.
- 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've undergone chemotherapy, you eat a high-protein diet or you have certain genetic factors that predispose you to the condition.
- Cystine stones. These stones represent only a small percentage of kidney stones. They form in people with a hereditary disorder that causes the kidneys to excrete excessive amounts of certain amino acids (cystinuria).
Risk factors :
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, work in a hot environment, such as a commercial kitchen, 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, sex and race. 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. In addition, white Americans are at higher risk of kidney stones than are black Americans.
- Certain diseases. Rare, inherited diseases such as renal tubular acidosis and cystinuria can increase your risk of kidney stones. So can more common disorders such as gout, chronic urinary tract infections and hyperparathyroidism.
- Certain medications. Medications can have variable effects on stone formation. For example, diuretics may increase your risk of developing kidney stones in some situations and decrease it in others. If you're at risk, check with your doctor or pharmacist about any medications you take.
- Diet. A diet that's high in protein (meat, chicken and fish) and sodium (salt), and low in whole grains and calcium 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 because limited activity can cause your bones to release more calcium.
You're not likely to have signs and symptoms unless a kidney stone is large, causes a blockage, is associated with an infection or is being passed. Then the most common symptom is an intense, colicky pain that may fluctuate in intensity over periods of five to 15 minutes. The pain usually starts in your back or your side just under or below the edge of your ribs. As the stone moves down the ureter toward your bladder, the pain may radiate to your lower abdomen, groin and genital structures on that side. If the stone stops moving, the pain may stop too. Other signs and symptoms may include :
- Bloody, cloudy or foul-smelling urine
- Nausea and vomiting
- Persistent urge to urinate
- Fever and chills if an infection is present
Although doctors may discover kidney stones during a routine medical exam, many kidney stones are diagnosed after a person complains of severe kidney pain, 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 :
- 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 computerized tomography (CT) scan but is still useful in limited circumstances.
- Spiral CT scan. This imaging test has become the standard of care for evaluating kidney stones. It's rapidly performed, can identify stones regardless of composition and doesn't require the use of contrast dye. The cost of the test and the amount of radiation exposure are limiting factors in the use of CT scanning.
If you're about to pass a stone, your doctor may ask you to urinate through a strainer so that the stone can be recovered and analyzed. The appropriate treatment and preventive measures depend on knowing what type of kidney stone you have.
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 infection 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 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 infection — 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 your 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.
Additionally, a study released in April 2006 showed that people treated with ESWL were more likely to develop high blood pressure and diabetes than people who received more conservative treatment for kidney stones. More study of ESWL will be needed to more clearly define the long-term risks.
- 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 can also 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.
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 of urine a day. To do this, you'll need to drink about 3.5 quarts (14 cups) of fluids every day — and even more if you live in a hot, dry climate. Although most liquids count, water is best.
In addition, if you tend to form calcium stones — a combination of calcium and oxalate — 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 the highest 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. When taken on an empty stomach, the calcium can't bind with the oxalates in food.
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.
- Cystine stones. Cystine stones are the hardest stones and the most difficult to treat. Your doctor may prescribe certain medications to alkalinize the urine or to bind the cystine in the urine in addition to recommending an extremely high urine output.