Kidney Stones Symptoms & Causes
One of the most painful urologic disorders, kidney stones, are also among the most common problems of the urinary tract. Each year, kidney stones are responsible for almost 3 million visits to doctors and clinics, and more than a half-million people go to emergency rooms for kidney stones annually.
Fortunately, most kidney stones pass out of the body without any doctor's intervention. Stones that cause lasting symptoms or other complications may be treated by various techniques, most of which do not involve major surgery. Also, research advances have led to a better understanding of the many factors that promote stone formation and thus better treatments for preventing stones.
What kidneys do
The kidneys are two bean-shaped organs located below the ribs toward the middle of the back, one on each side of the spine. The kidneys remove extra water and wastes from the blood, producing urine. Kidneys also keep a stable balance of salts and other substances in the blood.
The kidneys also produce hormones that help build strong bones and 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 within the urinary tract. 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. Kidney stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate. These chemicals are part of a person's normal diet and make up important parts of the body, such as bones and muscles.
A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone. Another type of stone, uric acid stones, are a bit less common, and cystine stones are rare. Urolithiasis is the medical term used to describe stones occurring in the urinary tract. Other frequently used terms are urinary tract stone disease and nephrolithiasis.
Doctors also use terms that describe the location of the stone in the urinary tract. For example, a ureteral stone-or ureterolithiasis-is a kidney stone found in the ureter. To keep things simple, the general term kidney stones is used throughout this fact sheet. Gallstones and kidney stones are not related. They form in different areas of the body. Someone with a gallstone is not necessarily more likely to develop kidney stones.
Symptoms of kidney stones
Kidney stones often do not cause any symptoms. Usually, the first symptom of a kidney stone is extreme pain, which begins suddenly when a stone moves in the urinary tract and blocks the flow of urine. 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 narrow ureter try to squeeze the stone into the bladder. As the stone moves and the body tries to push it out, blood may appear in the urine, making the urine pink.
As the stone moves down the ureter, closer to the bladder, a person 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, a person should contact a doctor immediately.
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. In the late 1970s, less than 4 percent of the population had stone-forming disease. By the early 1990s, the portion of the population with the disease had increased to more than 5 percent.
Caucasians 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, other stones 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, leading to the formation of stones made of cystine.
In patients with hyperoxaluria, the body produces too much oxalate, a salt. When the urine contains more oxalate than can be dissolved, the crystals settle out and form stones. Hypercalciuria is inherited, and it may be 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 elsewhere in the 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, commonly called water pills, and 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 chronic inflammation of the bowel or who have had an intestinal bypass operation, or ostomy surgery. As mentioned earlier, struvite stones can form in people who have had a urinary tract infection. People who take the protease inhibitor indinavir, a medicine used to treat HIV infection, may also be at increased risk of developing kidney stones.