Kidney stones, one of the most painful of the urologic disorders, are not a product of modern life. Scientists have found evidence of kidney stones in a 7,000-year-old Egyptian mummy. Unfortunately, kidney stones are one of the most common disorders of the urinary tract. In 2000, patients made 2.7 million visits to health care providers and more than 600,000 patients went to emergency rooms for kidney stone problems. Men tend to be affected more frequently than women.
Introduction to the urinary Tract
The urinary tract, or system, consists of the kidneys, ureters, bladder, and urethra. The kidneys are two bean-shaped organs located below the ribs toward the middle of the back. The kidneys remove extra water and wastes from the blood, converting it to urine. They also keep a stable balance of salts and other substances in the blood. The kidneys produce hormones that help build strong bones and help form red blood cells. Narrow tubes called ureters carry urine from the kidneys to the bladder, an oval-shaped chamber in the lower abdomen. Like a balloon, the bladder's elastic walls stretch and expand to store urine. They flatten together when urine is emptied through the urethra to outside the body.
What is a kidney stone?
A kidney stone is a hard mass developed from crystals that separate from the urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent or inhibit the crystals from forming. These inhibitors do not seem to work for everyone, however, so some people form stones. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without being noticed.
Gallstones and kidney stones are not related. They form in different areas of the body. If you have a gallstone, you are not necessarily more likely to develop kidney stones.
Who gets kidney stones?
For unknown reasons, the number of people in the United States with kidney stones has been increasing over the past 30 years. The prevalence of stone-forming disease rose from 3.8 percent in the late 1970s to 5.2 percent in the late 1980s and early 1990s. White Americans are more prone to develop kidney stones than African Americans. Stones occur more frequently in men. The prevalence of kidney stones rises dramatically as men enter their 40s and continues to rise into their 70s. For women, the prevalence of kidney stones peaks in their 50s. Once a person gets more than one stone, others are likely to develop.
What causes kidney stones?
Doctors do not always know what causes a stone to form. While certain foods may promote stone formation in people who are susceptible, scientists do not believe that eating any specific food causes stones to form in people who are not susceptible.
A person with a family history of kidney stones may be more likely to develop stones. Urinary tract infections, kidney disorders such as cystic kidney diseases, and certain metabolic disorders such as hyperparathyroidism are also linked to stone formation.
In addition, more than 70 percent of people with a rare hereditary disease called renal tubular acidosis develop kidney stones.
Cystinuria and hyperoxaluria are two other rare, inherited metabolic disorders that often cause kidney stones. In cystinuria, too much of the amino acid cystine, which does not dissolve in urine, is voided. This can lead to the formation of stones made of cystine. In patients with hyperoxaluria, the body produces too much of the salt oxalate. When there is more oxalate than can be dissolved in the urine, the crystals settle out and form stones.
Hypercalciuria is inherited. It is the cause of stones in more than half of patients. Calcium is absorbed from food in excess and is lost into the urine. This high level of calcium in the urine causes crystals of calcium oxalate or calcium phosphate to form in the kidneys or urinary tract.
Other causes of kidney stones are hyperuricosuria which is a disorder of uric acid metabolism, gout, excess intake of vitamin D, urinary tract infections, and blockage of the urinary tract. Certain diuretics which are commonly called water pills or calcium-based antacids may increase the risk of forming kidney stones by increasing the amount of calcium in the urine. Calcium oxalate stones may also form in people who have a chronic inflammation of the bowel or who have had an intestinal bypass operation, or ostomy surgery. As mentioned above, struvite stones can form in people who have had a urinary tract infection. People who take the protease inhibitor indinavir, a drug used to treat HIV infection, are at risk of developing kidney stones.
What are the symptoms?
Kidney stones often do not cause any symptoms. Usually, the first symptom of a kidney stone is extreme pain, which occurs when a stone acutely blocks the flow of urine. The pain often begins suddenly when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain in the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur. Later, pain may spread to the groin. If the stone is too large to pass easily, pain continues as the muscles in the wall of the tiny ureter try to squeeze the stone along into the bladder. As a stone grows or moves, blood may appear in the urine. As the stone moves down the ureter closer to the bladder, you may feel the need to urinate more often or feel a burning sensation during urination. If fever and chills accompany any of these symptoms, an infection may be present. In this case, you should contact a doctor immediately.
How are kidney stones diagnosed?
Sometimes "silent" stones—those that do not cause symptoms—are found on x rays taken during a general health exam. If they are small, these stones would likely pass out of the body unnoticed.
More often, kidney stones are found on an x ray or sonogram taken on someone who complains of blood in the urine or sudden pain. These diagnostic images give the doctor valuable information about the stone's size and location. Blood and urine tests help detect any abnormal substance that might promote stone formation. The doctor may decide to scan the urinary system using a special test called a CT (computed tomography) scan or an IVP (intravenous pyelogram). The results of all these tests help determine the proper treatment.
How are kidney stones treated?
Fortunately, surgery is not usually necessary. Most kidney stones can pass through the urinary system with plenty of water (2 to 3 quarts a day) to help move the stone along. Often, you can stay home during this process, drinking fluids and taking pain medication as needed. The doctor usually asks you to save the passed stone(s) for testing. (You can catch it in a cup or tea strainer used only for this purpose.) Stone may also be treated with the ESWL 'stone blasting' procedure.
The First Step: Prevention
If you've had more than one kidney stone, you are likely to form another; so prevention is very important. To prevent stones from forming, your doctor must determine their cause. He or she will order laboratory tests, including urine and blood tests. Your doctor will also ask about your medical history, occupation, and eating habits. If a stone has been removed, or if you've passed a stone and saved it, the laboratory should analyze it because its composition helps in planning treatment. You may be asked to collect your urine for 24 hours after a stone has passed or been removed. The sample is used to measure urine volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate, and creatinine (a product of muscle metabolism). Your doctor will use this information to determine the cause of the stone. A second 24-hour urine collection may be needed to determine whether the prescribed treatment is working.
A simple and most important lifestyle change to prevent stones is to drink more liquids — water is best. If you tend to form stones, you should try to drink enough liquids throughout the day to produce at least 2 quarts of urine in every 24-hour period.
People who form calcium stones used to be told to avoid dairy products and other foods with high calcium content. But recent studies have shown that foods high in calcium, including dairy products, may help prevent calcium stones. Taking calcium in pill form, however, may increase the risk of developing stones.
You may be told to avoid food with added vitamin D and certain types of antacids that have a calcium base. If you have very acidic urine, you may need to eat less meat, fish, and poultry. These foods increase the amount of acid in the urine. To prevent cystine stones, you should drink enough water each day to dilute the concentration of cystine that escapes into the urine, which may be difficult. More than a gallon of water may be needed every 24 hours, and a third of that must be drunk during the night.