Kidney Stones (Renal Calculi)

What is a Kidney Stone?

A kidney stone is exactly what its name implies: a hard, rock-like mass made of minerals in the kidney. Kidney stones are also known as “renal calculi.” “Calculi” is a general word for stones; “renal” refers to the kidneys. Because stones can travel through the urinary system, they can also be found in the ureters and bladder. (The symptoms and treatment of ureteral and bladder stones are essentially the same as that of kidney stones.)

Stones develop from chemicals filtered by the kidneys, such as calcium, uric acid and cystine. These substances can form crystals. Urine also contains other chemicals, such as citrate and magnesium that prevent crystals from forming. Usually, these substances balance each other. When they don’t, crystals can form and build up on the inner surfaces of the kidney. If enough crystals clump together, they form a stone. If the stone stays small enough, it can travel through the urinary tract and pass out of the body in the urine without being noticed.

Unfortunately, many stones continue to grow within the body. They can grow for months or even years before they cause a problem. But when they break off and start traveling into the ureter, they cause extreme pain. The pain, sharp and cramping, often begins suddenly and is felt in the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur. Later, the pain may spread to the groin.

Types of Kidney Stones

There are several types of kidney stones. Each consists of its own combination of chemicals and has its own set of causes. The types are described here. For causes, see Causes, Risk Factors and Prevention. The important point is that despite the differences in the composition and causes of stones, the symptoms they create and the way they are treated are usually very similar.

• Calcium stones
  This is the most common form of kidney stone, accounting for about 75% to 85% of all cases. The calcium is usually combined with oxalate and/or phosphate.
• Struvite (infection) stones
  This type of stone, far less common, is caused by urinary tract infections and is usually found more often in women. For more information about urinary tract infections, click here.
• Uric acid stones
  Even less common are stones made purely of uric acid, a by-product of protein metabolism.
• Cystine stones
  The least common type of stone, found in about 1% of cases, is made of cystine, an amino acid.

Symptoms

As mentioned above, stones may grow in the body for months or years without causing any symptoms. These “silent stones” may be discovered through x-rays taken during a general health exam and may pass out of the body easily.

However, the first symptom of kidney stones is often sudden, extreme pain, usually in the back and side in the kidney area, or in the lower abdomen. Other symptoms include:

• Nausea and vomiting
• Blood in the urine (hematuria): the blood may be visible, so that the urine appears reddish or darker than normal; or it may be microscopic and be discovered only when a urine sample is examined in a laboratory urine test (urinalysis)
• Frequent urge to urinate
• Burning sensation during urination
• Fever and chills (when infection is present)

Diagnosis

Usually, a person’s pain will send them to a doctor. The doctor will then order one or more diagnostic tests to check for kidney stones. These tests include:

• Blood and urine tests
  These help detect any abnormal substances that might cause stones to form.
• Imaging tests
  A number of imaging methods can be used to get images of the kidneys and other organs that show the stone’s size and location. These technologies include traditional x-rays as well as:
  • Intravenous pyelogram (IVP): This is a form of x-ray that allows a urologist to clearly see pictures of the urinary system (kidneys, ureters, and bladder). A special dye (called a “contrast agent”) is injected into a vein in the arm. It passes quickly into the urinary system, making it easier to see abnormalities there.
  • CT (Computed Tomography): Popularly known as a CAT scan, this uses computers to create detailed, three-dimensional cross-sectional pictures of the organs and areas being examined.
  • Ultrasound: This uses sound waves projected into the body to create pictures of the organs and areas being examined.

Treatment

It’s important to get treatment for kidney stones, even those that cause no pain, because they can damage the kidneys by blocking the flow of urine and causing bleeding and infection. Smaller stones can block the flow of urine through the ureters and urethra, causing urinary tract infection and other damage.

There are several ways to treat kidney stones:

• Passing the stone
• Extracorporeal shockwave lithotripsy (ESWL)
• Surgical approaches
  • Percutaneous nephrolithotomy (PNL)
  • Ureteroscopy (URS)
  • Parathyroid removal

Did You Know…

Kidney stones are very common. Each year, about one million new cases are reported in the U.S. About 10 percent of people in the United States will have a kidney stone at some point in their lives. Men tend to be affected more frequently than women.