Coping with Kidney Stones

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Passing a kidney stone, technically known as a renal calculus, can be excruciating - some women say it's more painful than childbirth. A stone lodged in the urinary tract may partly or completely block the flow of urine. Kidney stones can also lead to infection and, rarely, kidney failure.

About 4% of women develop kidney stones. Although more frequent in men, the condition (urolithiasis or nephrolithiasis) has become more prevalent among women during the past decade.

Fortunately, research has advanced our understanding of this problem. Years of data on thousands of women - for example, from the Nurses' Health Study (NHS) - have produced new theories on prevention. In addition, effective medications and less invasive surgical techniques have improved the prospects for treatment.

What are kidney stones?

Kidney stones develop when chemical compounds that are dissolved in the urine form solid crystals. This happens when urine volume is low or when abnormally high amounts of crystal-forming compounds are present. Sometimes an abnormality in the ureter wall provides a starting point for a stone. Dehydration can play a role and so can insufficient amounts of certain protective substances, such as magnesium and citrate.

The greatest risk factor for developing a kidney stone is having had one in the past - a person with a kidney stone has a 50% chance of forming others within 10 years. Kidney stones are also more common in people with a family history of the condition. Other risk factors include inherited kidney disorders, genetic defects, urinary tract infections, diseases or surgeries affecting the small intestine, and metabolic problems. In susceptible people, diet and certain medications can also be factors.

There are several types of kidney stones:

Calcium stones. About 80% of kidney stones contain calcium combined either with oxalate (a plant compound) or, less often, phosphate. Calcium stones are often familial, but a variety of genetic, dietary, and medical factors can cause excess calcium (hypercalciuria) or excess oxalate (hyperoxaluria) in the urine. Both conditions contribute to stone formation.
Struvite stones. Women are disproportionately affected by struvite stones, which account for 10%-15% of stones and are associated with certain urinary tract infections. Struvite is a glasslike mineral.
Uric acid stones. About 5%-8% of stones are made of crystallized uric acid, produced in the breakdown of meat and certain other foods. People with gout often have increased amounts of uric acid in the blood and urine.
Cystine stones. These stones are caused by a rare genetic disorder (cystinuria) that causes excess cystine and other amino acids in the urine.
Symptoms and signs

Most kidney stones are small enough to pass uneventfully in the urine. The trouble comes from the bigger ones and those with sharp edges.

If a stone gets wedged in the ureter, urine back ups, distending the ureter and triggering renal colic - intense pain that starts abruptly and comes in nauseating waves. It radiates across the upper back and may descend into the abdomen or pelvic area. The pain continues until the stone moves to a wider area, such as the bladder.

Most kidney stones cause bleeding. Even if the urine looks clear to the naked eye, microscopic examination usually reveals red blood cells.

If a stone blocks the flow of urine, pressure may build not only in the ureter but also in the kidney, causing it to swell - a condition known as hydronephrosis. In response, the kidney reduces its urine output. Unrecognized, hydronephrosis can permanently damage the kidney.

Diagnosing kidney stones

A clinician will take a medical and family history and do a physical exam. Blood and urine tests will also be ordered to check for infection, blood in the urine, or the presence of stone-forming substances.

Appropriate treatment depends on locating the kidney stone and determining its size and type. Until recently, specialists relied on an abdominal x-ray, which missed many stones; an intravenous pyelogram (IVP), which is accurate but requires an injection of dye into a vein to produce contrast x-rays of the urinary tract; or renal ultrasound, which requires no dye, but does not identify all kidney stones.

A major advance in diagnosing kidney stones is spiral computed tomography (spiral CT) scanning. Unlike IVP, a spiral CT scan requires no injection of dye, an advantage as the dye can cause allergic reactions. It's also fast and uses less radiation. The spiral CT scan can pinpoint more types and sizes of stones than any other procedure. Unfortunately, spiral CT scanning is not widely available.

Treating kidney stones

The first step is to relieve pain, with nonsteroidal antiinflammatory drugs or painkillers such as narcotics. The next step is to get rid of the stone or stones.

If it's likely that the stone will pass out of the body within 72 hours, physicians usually recommend extra fluids - two to three quarts of water a day to help flush it out - along with pain medication. A stone of 5 millimeters (about one-fifth inch) in diameter or less rarely requires special intervention. Passing even a small stone may take a while (from a couple of days to several weeks) and can cause considerable pain as it moves through the urinary tract. Your clinician will probably advise you to strain your urine to catch any stones so they can be analyzed.

Multiple or bigger stones, severe pain, and infection require different approaches.

Extracorporeal shock wave lithotripsy focuses high-energy sound waves on the kidney stones from a device known as a lithotriptor, fragmenting them into pieces small enough to pass through the urinary tract. Lithotripsy is an outpatient procedure that requires strong sedation but not general anesthesia. It works best on stones located in the kidney or upper ureter that are smaller than 1.5 centimeters.
Percutaneous nephroureterolithotomy uses a tube inserted through the skin into the kidney to reach stones too large or dense for lithotripsy. The technique is also used to treat struvite stones, which could spread infection if they were simply broken up by lithotripsy. An ultrasonic tool breaks up the stone and suctions out the pieces. This outpatient procedure also requires sedation.
A ureteroscope locates stones caught in the lower part of the ureter. Instruments inserted through the ureteroscope can grasp the stone or pulverize it with a laser.
Medication may help dissolve uric acid or cystine stones.
How To Prevent Recurrences

The Nurses' Health Study suggests that plenty of fluids and a diet rich in calcium and potassium benefit every woman. But women trying to avoid recurrences of kidney stones need to take further measures, under medical supervision.

Medications often help. For calcium-based stones, indapamide, chlorthalidone, thiazide, trichlormethiazide, and hydrochlorothiazide may be useful. Potassium-magnesium citrate and potassium citrate also inhibit stones. Allopurinol lowers uric acid levels.
Increased fluid intake helps dilute substances that spur stone formation, especially calcium stones. This means drinking two to three quarts of fluid per day, and more if you exercise. Nurses' Health Study researchers found that women who drank almost three quarts per day had a lower risk of stone recurrence than those who drank half that amount. The risk decreased with wine and with caffeinated and decaffeinated coffee and tea, but rose with grapefruit juice. Many fluids are helpful, but experts suggest choosing water at least half the time. They also recommend awakening at night to urinate and drink more water.
Dietary changes such as limiting sodium intake to no more than 2,000 mg a day are also advised. Diets high in potassium and low in sugar also reduce the risk. Women at risk for uric acid stones should limit intake of foods that contain purines: alcoholic drinks, anchovies, sardines, organ meats (liver, kidney, and heart, for example), dried beans and peas, spinach, asparagus, cauliflower, and poultry. But unless advised by a doctor, people with calcium oxalate stones need not limit their consumption of dietary oxalate (found in rhubarb, spinach, parsley, Swiss chard, beets, chocolate, and tea).
Vitamin B6 - at least 40 mg a day - may help prevent kidney stones by slowing oxalate production.
Calcium and Kidney Stones

Because kidney stones contain calcium, women with kidney stones have been told to restrict their intake of calcium - advice that can lead to low bone mineral density. But surprisingly, two recent Harvard Medical School studies indicate that calcium-rich foods protect against stones. Calcium is thought to bind to dietary oxylate in the digestive tract and help remove it from the body. When dietary calcium is low, more oxylate reaches the urine, where it combines with excess urinary calcium to form kidney stones.

Supplemental calcium may be different. One study showed that women who regularly took calcium supplements had a 20% higher than average risk of stone formation. Possibly the supplements were taken between meals when there was no oxalate in the gut to bind the calcium (leaving more available in the body). It's also possible that dairy foods, the major source of dietary calcium, contain an unidentified protective substance not found in supplements.

Generally, women should continue to get 1,200 mg of calcium per day through food and supplements. But if you have had kidney stones, you should contact your primary care provider to discuss what's appropriate in your case. You may find this reference helpful: Curhan GC et al. "Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women," Annals of Internal Medicine, 1997 April 1;126(7):497-504.

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