INTRODUCTION

Kidney stones (also called nephrolithiasis or urolithiasis) develop when a collection of minerals or other material form a small "stone." The stone can cause pain, block the flow of urine, and rarely cause long-term kidney problems if it is not recognized and treated promptly. Fortunately, most children who develop kidney stones recover without any long-term complications.

Stones are less common in children than in adults. Most children who develop kidney stones have an underlying condition that increases their risk of stones, although some children develop a stone for unknown reasons.

A discussion of kidney stones in adults is available separately. (See "Patient information: Kidney stones in adults (Beyond the Basics)".) More detailed information about kidney stones in children is available by subscription. (See "Acute management of nephrolithiasis in children".)

HOW KIDNEY STONES DEVELOP

The urinary tract is composed of two kidneys and ureters, a bladder, and a urethra (figure 1). A kidney stone usually forms when substances that are normally found in the urine, such as calcium, oxalate, cystine, or uric acid, are at high levels. However, in some children, stones can also form if these substances are at normal levels. Knowing what the stone is made of is important in deciding which treatment to use (see 'Stone testing' below).

The substances form crystals, which become anchored in the kidney and gradually increase in size, forming a kidney stone. Stones that are very small (less than 5 millimeters (0.2 inches)) can usually pass on their own, while larger stones usually require treatment.

A kidney stone moves through the urinary tract and, if it is small enough, it will be passed in the urine. A larger stone can become stuck within the urinary tract, causing pain and sometimes blocking the flow of urine.

KIDNEY STONE SYMPTOMS

The most common symptoms of kidney stones include:

• Pain in the belly or back (figure 2)
• Blood in the urine (hematuria)
• Nausea or vomiting
• Needing to rush to the bathroom to urinate

However, some children, particularly young children, do not have any symptoms, and the kidney stone is found when an imaging test (like an X-ray) is done for another reason.

Some kidney stone symptoms are similar to those of a bladder infection (also called a urinary tract infection). Your child's doctor or nurse will need to perform an exam and do some testing to know what is causing the symptoms. (See "Patient information: Urinary tract infections in children (Beyond the Basics)".)

KIDNEY STONE RISK FACTORS

Certain factors can increase a child's risk of developing kidney stones. (See "Epidemiology of and risk factors for nephrolithiasis in children".)

• History of kidney stones – Children who have had a kidney stone in the past have the highest risk of developing a stone in the future. Preventive measures can decrease the risk of developing a stone in the future. (See 'Kidney stone prevention' below.)
• Not drinking enough – The amount of fluids a child drinks directly affects the amount of urine the body makes. Drinking a small amount of fluids means that the kidneys make a small amount of urine, which increases the concentration of stone-forming substances in the urine. Drinking more fluids can reduce the risk of recurrent stones. (See 'Drink more fluids' below.)
• Ketogenic diet – Diets that include a very small amount of carbohydrates, called ketogenic diets, can increase the risk of developing kidney stones. Ketogenic diets are sometimes used to treat seizure disorders. (See "Patient information: Treatment of seizures in children (Beyond the Basics)".)
• Cystic fibrosis – Children with cystic fibrosis are at higher risk of developing kidney stones.
• Urinary tract abnormalities – Having congenital (from birth) abnormalities in the kidneys, ureters, or bladder can increase the risk of developing a kidney stone.
• Medicines – Some medicines increase the risk of forming crystals in the urine. These include furosemide (Lasix), acetazolamide (Diamox), and allopurinol (Aloprim, Zyloprim).
• Inherited disorders – Several uncommon inherited disorders can increase a child's risk of developing kidney stones. Testing for these disorders might be recommended.

KIDNEY STONE DIAGNOSIS

If your child has symptoms of a kidney stone, he or she should see a doctor or nurse as soon as possible. The doctor or nurse will do an exam and order urine testing.

If a stone is likely, based on the exam and urine tests, he or she will order an imaging test, like a CT scan, ultrasound, or X-ray. The imaging test can show the exact size and location of the stone, which will help to guide treatment. (See "Clinical features and diagnosis of nephrolithiasis in children".)

KIDNEY STONE TREATMENT

Treatment at home — If the stone is small, pain is manageable, and the child is otherwise healthy, it is often possible to treat the stone at home. Stones smaller than 5 millimeters (0.2 inches) often pass on their own without treatment.

You can treat your child's pain with a non-prescription medicine like ibuprofen (sold as Advil®, Motrin®, and store brands). The child should also drink more fluids than usual to help flush the stone out. (See 'Drink more fluids' below.)

You will need to strain your child's urine for a few days, until the stone passes. Urine strainers are available from most hospital supply stores. You place the strainer under the toilet seat. If you cannot find a urinary strainer, you can use a toilet hat covered with cheese cloth or a fine mesh sheet. A fish net used for home aquariums is also a good alternative.

If the child passes a stone or stone fragment, save it in a clean container. A lab can analyze the stone to determine the type, which can guide treatment. After the child passes the stone, a follow-up test (usually ultrasound) might be done to confirm that the stone is gone and that no other stones or stone fragments are left.

Hospital treatment — In some cases, the child will need to be hospitalized for treatment. The two most common reasons for hospitalization are that:

• The stone is blocking the urinary tract, preventing the normal flow of urine. If the blockage is not treated quickly, it can cause permanent damage to the kidneys.
• The child's pain cannot be controlled because it is severe or because the child is vomiting.

In the hospital, the child will be given intravenous (IV) pain medications and IV fluids. If the stone is small, this treatment may be continued for several days, until the stone passes. During this time, the location of the stone is usually monitored with ultrasound. The child's urine will be strained to recover any stone or stone fragments that pass.

However, stones larger than 9 or 10 millimeters (about half an inch) rarely pass on their own and generally require treatment. Other reasons for treatment include severe pain and if the stone is blocking the urinary tract.

Treatments to eliminate the stone — One or more treatments can be used to eliminate a kidney stone. Shock wave lithotripsy is the first-line treatment in most cases.

• Shock wave lithotripsy – Shock wave lithotripsy is the treatment of choice for kidney stone in many children. Lithotripsy is done by directing a high-energy shock wave toward the stone. The energy causes the stone to break into fragments that can be passed. The procedure takes about 20 minutes. Some, although not all, children are given anesthesia to prevent movement during the treatment.
  
  The success of lithotripsy depends, in part, on the size of the stone; larger stones are more difficult to break up and sometimes need more than one treatment. It can take three months after lithotripsy for all of the stone fragments to pass.
• Percutaneous nephrolithotomy – Large stones or stones that do not break up with lithotripsy will require a minimally invasive surgical procedure to remove the stone. During the procedure, small instruments are passed through the skin (percutaneously) into the kidney to remove the stone. The child is given anesthesia before the procedure to prevent pain.
• Ureteroscopy – Ureteroscopy is a procedure that can be done if the stone is in the middle and lower portion of the ureter (figure 1). A doctor passes a small instrument through the urethra and bladder, into the ureter. The instrument contains a camera and other instruments, which allows the doctor to see the stone. The stone can be removed or broken up into smaller pieces that can pass more easily.

Will my child have kidney problems in the future? — The chances of developing kidney stones, kidney damage, and other complications after a first kidney stone depend largely on the child's age at the time of the first stone and the underlying reason that the stone developed.

KIDNEY STONE PREVENTION

Children who develop a kidney stone have a significant chance of developing stones in the future. Studies have estimated the chances to be between 30 and 65 percent [1]. However, a number of steps can decrease the chances of developing another stone. (See "Prevention of recurrent nephrolithiasis in children".)

Blood and urine tests — After a child has had a kidney stone, blood and urine tests are performed to identify factors that can increase the risk of future stones. Testing is not done until the child is at home, walking and playing normally, eating a normal diet, and has finished any treatment for urinary tract infection.

You might be asked to collect your child's urine for 24 hours. (See "Patient information: Collection of a 24-hour urine specimen (Beyond the Basics)".)

Stone testing — If the stone was passed and saved, it should be analyzed to determine the type of stone. Based on what the stone is made of, one or more treatments might help to reduce the risk of future stones (see 'Treatment' below).

Drink more fluids — Drinking more fluids can help to decrease the risk of forming all types of kidney stones. The goal is to increase the amount of urine that flows through the kidneys and ureters and to lower the concentration of substances that promote stone formation.

To gauge how much more fluid the child should be drinking, your doctor or nurse might recommend measuring how much urine the child passes over the course of 24 hours. The child should drink more if he or she makes less than this amount of urine per 24 hours.

• Infants – 750 mL or more (25 ounces or three cups)
• Children younger than five years of age – 1000 mL or more (33 ounces or four cups)
• Children between five and ten years of age – 1500 mL or more (50 ounces or six cups)
• Children greater than 10 years of age – 2000 mL or more (66 ounces or eight cups)

Treatment — One or more treatments might be recommended to decrease the risk of developing another kidney stone in the future. The best treatment depends on what minerals or other materials were found in the first stone (see 'Stone testing' above).

Calcium — Children with increased levels of calcium in the urine should drink more fluids and make some changes in their diet:

• Eat a low-sodium diet (figure 3 and table 1)
• Get the right amount of calcium from foods and drinks. The amount of calcium in selected foods is provided in the following table (table 2). Consuming too much calcium in foods and drinks is not recommended. However, the child should not stop eating foods and drinks with calcium because calcium is important in building strong bones.
  
  The "right" amount of calcium depends on the child's age:

• 500 mg/day for children one to three years
• 800 mg/day for children four to eight years
• 1300 mg/day for children nine years and older

• Avoid calcium and vitamin D supplements
• Eat potassium-rich foods (fresh fruits and vegetables)
• If urine calcium levels are still high after three to six months of these changes, a medicine might be recommended

Oxalate — Children who have high levels of oxalate in the urine should:

• Drink more fluids
• Avoid vitamin C supplements
• Avoid foods that contain large amounts of oxalate, including beet and turnip greens, rhubarb, strawberries, star fruit, sweet potatoes, wheat bran, tea, cocoa, pepper, chocolate, parsley, beets, spinach, dill, nuts, and citrus juices

Urate — Children with increased levels of urate in the urine should drink more fluids. Some children will be given a treatment to increase the pH of the urine (potassium citrate or potassium carbonate).

Cystine — Children with high levels of cystine in the urine should drink more fluids. Some children will be given a medicine that reduces the acidity (ie, increases the pH) of the urine (potassium citrate or potassium carbonate).

Low citrate — Children who have a low level of citrate in the urine are usually given a treatment to increase citrate levels (potassium citrate or potassium bicarbonate).

Struvite — Struvite stones usually develop because of a urinary tract infection. Preventing future urinary tract infections can help to prevent struvite stones. This is discussed separately. (See "Patient information: Urinary tract infections in children (Beyond the Basics)".)

Complementary and alternative therapies — There are no data about the safety or benefit of complementary and alternate therapies for kidney stones in children (including herbs, homeopathy, acupuncture, and others). We do not recommend these therapies because they are unproven.

Monitoring — After a first kidney stone, the child's doctor or nurse might recommend an imaging test (like ultrasound) to monitor for new stones. This is especially important for children who are at high risk of kidney stones.

WHERE TO GET MORE INFORMATION

Your child's healthcare provider is the best source of information for questions and concerns related to your child's medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient information: Kidney stones in adults (The Basics)
Patient information: Kidney stones in children (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

This topic currently has no corresponding Basic content.

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

• National Library of Medicine

     (www.nlm.nih.gov/medlineplus/healthtopics.html)

[1-4]