Kidney stones

Kidney stones are stones that form in the kidneys. They can lodge anywhere in the urinary tract.


Anatomy
Normally, a person has two kidneys. The main function of the kidneys is to filter waste products from the blood and help eliminate them from the body. Each kidney has a ureter, a tube that drains urine from the kidney to the bladder. Urine collects in the bladder, and then it drains through the urethra and out of the body. Together, these body parts form the urinary tract.

Causes/associated factors
Kidney stones develop when crystals in the urine accumulate in the kidney and form deposits. Chemicals in the urine normally prevent this process, but the chemicals may be ineffective if you have:
an underlying medical condition
concentrated urine usually resulting from limited fluid intake
a change in the urine's pH (too alkaline or too acidic)
a lack of natural substances in the urine that are supposed to prevent stone formation
About 10 percent of people in the United States develop kidney stones at some point. The risk of developing kidney stones is highest for Caucasians, males between ages 20 and 40 and people who:

have a family or personal history of kidney stones
have certain medical problems, such as urinary tract infections, cystic kidney disease, overactive parathyroid gland, gout, chronic diarrhea or an intestinal bypass or ostomy
have certain inherited conditions, such as hypercalciuria, renal tubular acidosis, cystinuria or hyperoxaluria
take certain medications, such as antacids containing calcium, certain diuretics or medications to treat HIV, the virus that causes AIDS
drink few fluids
live in an area with high humidity and high temperatures, which contributes to dehydration (such as the southeastern United States)
eat a diet high in animal protein or salt
have a sedentary lifestyle
Here's a description of the four most common types of kidney stones.

Calcium stones
Up to 75 percent of kidney stones are calcium stones. When you have calcium stones, there's an excessive amount of calcium in your urine. This may occur for various reasons. For example, your body may absorb too much calcium from your bones or the food you eat. This can be related to factors such as:

hyperparathyroidism (an excessive secretion of parathyroid hormone that causes a high calcium level in your blood)
sarcoidosis (a disease in which abnormal collections of inflammatory cells form in a variety of organs)
certain kidney conditions
taking certain medications
getting too much vitamin D
Uric acid stones
Uric acid stones mainly develop in men. These stones may occur when the urine is too acidic. People who have uric acid stones often have a history of gout (a disorder that causes sudden, recurring attacks of painful arthritis). Other people who develop uric acid stones may have a history of rapid weight loss or a diet rich in meat. Certain types of cancer or chemotherapy treatment may also lead to uric acid stones.

Struvite stones
Struvite stones, also called infection stones, only develop in the high-alkaline environment of infected urine. These stones develop more often in women who have repeated urinary tract infections.

Cystine stones
Cystine is one of the building blocks that make up muscles, nerves and other parts of the body. Cystine stones are caused by cystineuria, a hereditary defect that leads to large amounts of cystine crystals in the urine. It's very difficult to prevent recurrences of these stones.


Signs/symptoms
Symptoms can vary widely depending on the location, shape and size of the stones. Some people have no symptoms at all. For many, however, the classic symptoms are severe pain and the inability to lie still, typically when a stone moves through the urinary tract.
Other symptoms may include:

a persistent urge to urinate
pain or burning sensation associated with urination
intense pain radiating from the lower back to the abdomen, pelvis and into the scrotum or labia
nausea
vomiting
blood in the urine
fever or chills if an infection is present

Diagnosis
Diagnosis is based on your symptoms and a physical exam. Your doctor may also recommend a few simple tests.
Your urine may be evaluated through a urinalysis, urine culture or 24-hour urine specimen. These tests allow the doctor to check for blood, crystals and bacteria, as well as the pH and chemical formation in your urine.

Blood tests may also be done to help evaluate how well your kidneys are functioning and if you're properly hydrated.

An abdominal X-ray, renal ultrasound (using sound waves to outline the stones) or computed tomography (CT scan, a computer- generated, cross-sectional picture of internal body parts) may be done to help diagnose or locate the position of the stone.

Your doctor may also suggest an intravenous pyelogram (IVP). After injecting a contrast dye into your system, the doctor takes X-rays of your kidneys. This procedure helps the doctor see if stones, a tumor or anatomic abnormalities are restricting or blocking urine flow, as well as find stones that may be missed with a standard X-ray.

Treatment
If you have mild symptoms or no symptoms at all, the doctor may recommend watchful waiting. Although it can be painful, most kidney stones pass through the urinary tract on their own without causing complications or permanent damage.
You may need treatment if you develop symptoms or the stones grow very large. Treatment varies, depending on the severity of the condition and the location, shape, size and type of stones. The goals are the same, however -- to relieve pain and obstruction, treat infection, and prevent kidney damage and the recurrence of stones. Treatment may include any combination of the following elements.

Self-care
Drinking plenty of fluids can dilute your urine and help the stone move through your urinary tract. You may be asked to drink 2 to 3 quarts of water a day. You may also be asked to collect and strain your urine and save any stones you find. To determine their composition, the stones can be sent to a lab for analysis. This information may reveal the cause of your kidney stones and help your doctor plan the best treatment to prevent future stones. You may need a prescription medication to control your pain and an antibiotic if you have a urinary tract infection.

Medical procedures
If your kidney stones don't pass and cause a urinary obstruction, damage to the kidney or constant pain, bleeding or infection, you may need more aggressive treatment.

Extracorporeal shock wave lithotripsy (ESWL) uses external high-energy sound waves directed toward the stone in your body. As they travel into the tissues, the sound waves hit the stones and break them into small pieces that are more easily passed through urination. This procedure is effective for stones in the kidney and upper part of the ureter. ESWL is typically done on an outpatient basis. It can be painful, so anesthesia is usually given.

Percutaneous nephrostolithotomy (PNL) is used to remove large kidney stones and is used if ESWL isn't successful. First, you'll receive anesthesia. Then, a thin scope will be inserted through the skin and into the kidney. Special instruments may be used to break up the stones. The pieces can be removed with the help of fluoroscopy, a type of X-ray. You'll need to stay in the hospital for a few days, sometimes with a tube draining the kidney. Since the stones are removed, you won't pass them through urination.

Urethroscopic stone removal involves removing the stone with a fiberoptic instrument passed into the urethra, through the bladder, and into the ureter. This procedure is used for stones in the middle and lower parts of the ureter. It's usually done on an outpatient basis.


Complications
Complications of kidney stones may include:
serious kidney infections that may require hospitalization
kidney damage
kidney failure if the kidney stones cause complete obstruction

Pregnancy-specific information
Pregnancy is not a risk factor for the development of kidney stones.

Senior-specific information
Growing older is not a risk factor for this condition.

Prevention
To prevent kidney stones, work with your doctor to correct any underlying causes. Drink plenty of fluids, especially water. Try to prevent dehydration, especially during warm weather. Your doctor may prescribe medication to keep new stones from forming. You may also be given a special diet to reduce crystal formation in the kidney.
Your doctor may prescribe medication to keep new stones from forming. Depending on the type of stones and their underlying cause, medications can:


control urine pH
decrease urine concentration
prevent urinary tract infections
prevent certain types of stones from forming
Depending on the type of kidney stones you have, your doctor may also recommend adjusting your diet. Ask your doctor for details.