Kidney Stones - Harvard Women's Health

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Women's Health Watch - Harvard Health

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Harvard Women's Health Watch

November 2001

 

Coping with Kidney Stones

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 backs up, 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.

 

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.

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.