The urinary tract 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, one on each side of the spine. The kidneys remove extra water and wastes from the blood, producing 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 form red blood cells.
What Is a Kidney Stone?
A kidney stone is a solid piece of material that forms from crystallization of excreted substances in the urine. The stone may remain in the kidney or break loose and travel down the urinary tract. A small stone may pass all of the way out of the body, but a larger stone can get stuck in a ureter, the bladder, or the urethra. This may block the flow of urine and cause great pain.
A kidney stone may be as small as a grain of sand or as large as a pearl, and some are as big as golf balls. They may be smooth or jagged, and are usually yellow or brown in color.
UC San Diego Health's Kidney Stone Center offers comprehensive treatment for kidney stones.
What Are Symptoms of a Kidney Stone?
Depending on a kidney stone's size and shape, it may pass easily by itself without any symptoms. When a stone is not passed easily, the first symptom is usually extreme pain, which begins suddenly when a stone moves in the urinary tract and blocks the flow of urine.
Generally, symptoms may include:
- Severe pain on one side of the back, just below the rib cage (flank pain) as well as the lower abdomen, groin, and genital area
- Nausea and vomiting
- Blood in the urine
- Urge to urinate more often
- Burning sensation during urination with fever and chills, which may indicate infection
What Are Kidney Stones Made of?
Kidney stones can be made of different compounds. Knowing a stone's composition will help your provider treat it effectively. The four general types of kidney stones are:
Calcium stones: Nearly 80 percent of all kidney stones are made of calcium compounds, especially calcium oxalate. Conditions that cause high calcium levels in the body, such as hyperparathyroidism, increase the risk of calcium stones.
Uric acid stones: Between 5 and 10 percent of kidney stone are formed from uric acid, a waste product normally passed out of the body in the urine. Causes include low urine output, gout and a diet high in animal protein.
Struvite stones: Approximately 10 to 15 percent of kidney stones are struvite stones. Struvite stones can be serious because they are often large stones and may occur with an infection. Medical treatment, including antibiotics and removal of the stone, is usually needed for struvite stones. In general, women are more susceptible to these stones than men because of their higher risk of urinary tract infections.
Cystine stones: Less than 1 percent of kidney stones are made of a chemical called cystine. Cystine stones are more likely to develop in families with a condition that results in too much cystine in the urine (cystinuria). These stones can sometimes be prevented or dissolved with medication, but if the stones cause blockage in the urinary tract or are too large, then surgical removal will be necessary.
Who Is Likely to Get Kidney Stones?
- Caucasians are more prone to kidney stones than African-Americans.
- Although stones occur more frequently in men, the number of women who develop kidney stones has been increasing.
- Kidney stones strike most people between the ages of 20 and 40.
- People with a family history of kidney stones are at greater risk of developing them.
- People with high blood pressure, gout and certain other medical conditions are at higher risk.
- Once you get a kidney stone, you are more likely to develop additional ones.