Kidney stones are small, solid masses that can develop in the urinary tract. Also called calculi or nephrolithiasis, kidney stones form when salts and minerals in urine (pee) become extra concentrated and form crystals. Over a few weeks or months, the crystals can build up and become stones.
Kidney stones range in size from a fraction of an inch to several inches. Small kidney stones (0.2 inches or less than 5 mm) can pass through the urinary tract and out of the body with little or no pain, but larger stones can be quite painful, block the flow of urine, and cause blood in the urine and other symptoms. In some cases, kidney stones can lead to problems with the kidneys and urinary tract. Most kidney stones, however, cause no permanent damage.
Though they occur most often in adults, kidney stones are fairly common in kids. There are different types of kidney stones with many different causes, with most types more common in males than females.
Treatment depends on the type of stones and their size. Some kids just need to drink a lot of water and take pain medications to pass a kidney stone. Those with larger stones may need surgery or other treatments to help remove the stones from their urinary tracts.
How Kidney Stones Form
It's the kidneys' job to remove excess fluids and waste products from the blood and pass them through the urinary tract and out of the body as urine (pee). Urine contains substances — such as calcium, oxalate, phosphate, carbonate, cystine, and uric acid — that in large amounts can crystallize and form kidney stones.
Usually, these substances are very diluted in the urine. But if urine becomes concentrated or something changes the level of a substance in it, crystals can begin to form. The crystals can become lodged in kidney tissue and grow to become kidney stones.
Types of Kidney Stones
Different substances in the urine can cause different kinds of kidney stones. The four major types of kidney stones are:
- Calcium stones: The most common kind of kidney stone, these develop when calcium in the urine combines with other substances to form crystals.
- Cystine stones: These are rare and form when there is too much cystine (an amino acid) in the urine.
- Uric acid stones: These form when there is too much uric acid in the urine. Uric acid can crystallize by itself or combine with calcium to form a stone.
- Struvite stones: Also called staghorn calculi because they look like a stag's antlers, these are made of a mineral called struvite that consists of ammonium, magnesium, and phosphate. Struvite stones almost always are due to an infection of the kidneys or urinary tract. More common in females, these can grow rather large and be more harmful to the kidneys than other stones.
Kidney stones are more common in adults, but premature babies, kids, and teens can still get them.Most kids who develop them have a health condition that increases their risk for kidney stones. Others develop them for unknown reasons.
Some types of kidney stones run in families, so having a relative with kidney stones can make someone more likely to develop them. Kids who have had kidney stones before face a greater risk of getting them again.
Other risk factors include:
- Dehydration. Not drinking enough fluids can make urine become extra concentrated and increase the likelihood of crystals forming.
- An unhealthy diet and lifestyle. Drinking sugary or caffeinated beverages and eating a diet high in sodium can increase the risk of calcium stones. Obesity can also make kids more likely to get them.
- Urinary tract defects. A defect in the urinary tract can obstruct the flow of urine and create an area where it collects in a tiny pool. When urine stops flowing, crystal-forming substances may settle together and form stones.
- Taking certain medications. Some prescription and over-the-counter medicines can increase the risk of kidney stones if taken in large doses.
- Metabolic disorders. Having a metabolic disorder (a problem in the way the body breaks down and uses food) can lead to concentrated levels of oxalate (a substance made in the body and found in some foods) or cystine in the urine.
- Cystinuria. This genetic condition causes too much cystine to pass from the kidneys into the urine, causing cystine stones to form.
- Other medical conditions. A number of diseases and conditions can increase the risk of kidney stones, including gout (a type of arthritis), other kidney diseases, conditions that affect the thyroid or parathyroid gland, and some urinary tract infections (UTIs).
Signs & Symptoms
Usually, kids with kidney stones won't have any symptoms until the stones move around in the kidney or pass into the ureter. Small stones might pass through the urinary tract and out of the body with no pain or complications.
Larger stones, however, may block the urinary tract and can cause symptoms like:
- sharp pain that starts in the side or back
- pain that spreads to the lower abdomen and groin as stones move through the urinary tract
- pain that comes and goes in waves
- blood in the urine (red or brown urine), called hematuria
- nausea and vomiting
- frequent or urgent need to urinate
- fever or chills
In some cases, a stone that's too large to move can cause an obstruction called hydronephrosis, or swelling in one kidney due to a backup of urine. Hydronephrosis can cause pain in the side and back. If it's not treated, it may cause long-term damage to the kidney.
If your child has pain in the side, blood in the urine, or any other symptoms of kidney stones, see a doctor as soon as possible. If your child has pain along with nausea, vomiting, fever, or chills, or is having trouble peeing, seek immediate medical attention at an emergency clinic or hospital emergency room.
To make a diagnosis of kidney stones, the doctor will ask about the symptoms and how long they've been going on; your child's diet; factors that could be causing dehydration; any family history of kidney stones; and any history of diseases or conditions that can affect the kidneys or urinary tract.
The doctor will do a physical exam and probably order blood, urine, or kidney function tests to see if kidney stones are present. Imaging tests (such as ultrasounds, X-rays, or CT scans) are often used to get a better look at the kidneys. If there is a stone, an imaging test can show its exact size and location, which will help doctors decide on the best treatment.
Treatment for kidney stones depends on the type of stones, the condition causing them, and how severe the symptoms are. Small stones usually pass on their own and don't need much treatment, but large stones may require surgery or another procedure to help remove them.
To help pass a small stone, encourage your child to drink plenty of water and consider giving medications to ease the pain. Often, over-the-counter medicines such as ibuprofen and acetaminophen are enough, but some cases may require prescription pain medications. The doctor also may ask you to strain your child's urine for a few days to collect the passed kidney stones. Examining the stones can help the doctor decide on the best treatment.
Kidney stones that block the urinary tract or cause severe pain or dehydration may require a hospital visit. In the hospital, a child may be given intravenous (IV) fluids and pain medications to help stones pass and treat or prevent dehydration.
Large stones rarely pass on their own and generally require more aggressive treatment. Treatments doctors use to eliminate large stones and stones that are damaging the kidneys include:
- Extracorporeal shock-wave lithotripsy. This treatment uses sound or shock waves to break kidney stones into smaller pieces that can be passed out of the body in urine.
- Ureteroscopic stone removal. In this procedure, a long, thin tube called a ureteroscope is inserted into the urethra and fed into the ureter (a tube that connects the bladder and kidney). Ureteroscopes are equipped with tiny cameras that can help doctors see a kidney stone. Once the stone is located, the ureteroscope has special tools that can remove the stone from the urinary tract or break it into smaller pieces that can be passed in the urine.
- Percutaneous nephrolithotomy. This technique is used for large stones in or near the kidneys. A tube called an endoscope is inserted into the kidney through a small surgical cut in the back and used to remove the stone. For large stones, an ultrasonic probe may be needed to deliver shock waves that break the stone into small pieces that can be removed more easily. Percutaneous nephrolithotomy often requires a hospital stay of 1-2 days after the procedure.
- In rare cases, if any of the above techniques don't work, a type of open surgery called nephrolithotomy may be done to remove large stones. This involves making a cut or incision in the side to gain access to the kidney. X-rays taken during this procedure help surgeons locate the kidney stone. Once the stone is identified, it is removed and sent to a lab for testing.
If your child has been treated for kidney stones, doctors will want to find out if he or she is at risk for developing more stones. Once any treatment has ended and your child is back to eating, drinking, and performing normal activities, urine or blood tests will be recommended.
Urine is usually tested through a 24-hour urine collection, which measures the volume of urine your child pees out within a 24-hour period and evaluates the substances in it. Depending on the outcome of this test, and any blood tests, additional treatment might be recommended to prevent future stones.
While it's not always possible to prevent some types of kidney stones, drinking enough water to avoid dehydration is important. When pee is almost clear, it's a sign that a person is getting enough fluids. Cutting back on salt and salty foods also helps lower the risk of kidney stones.
To help prevent new stones from forming, all kids who've had kidney stones should:
- drink a lot of fluids throughout the day. This can mean anywhere from 3 cups of fluid a day (for infants) to 8 cups a day (for teens). Ask your doctor how much your child should drink.
- limit the amounts of salt and protein in their diet
- limit consumption of soda/soft drinks
If dietary changes fail to prevent kidney stones, drug therapy might be helpful. A number of drugs are available to reduce the levels of crystal-forming substances in the urine and prevent the formation of kidney stones.
Reviewed by: Robert S. Mathias, MD
Date reviewed: May 2013