Patient information: Kidney stones in children

KIDNEY STONES OVERVIEW

Kidney stones (also called nephrolithiasis or urolithiasis) develop when a collection of minerals or other material form a small "stone" in the kidney, ureter, or bladder. The stone can cause pain, block the flow of urine, and 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, although the number of children who develop stones is unclear. 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.

This topic review discusses how and why kidney stones develop, and the symptoms, diagnosis, treatment, and ways to prevent a recurrence of kidney stones. A topic review that discusses kidney stones in adults is available separately. (See "Patient information: Kidney stones in adults".)

HOW KIDNEY STONES DEVELOP

A brief overview of the anatomy of the urinary tract will help to explain how kidney stones develop. The urinary tract is composed of two kidneys and ureters, a bladder, and a urethra (figure 1). Urine is produced by the kidneys, which are located towards the middle of the back, below the ribs.

The kidneys remove waste products and excess fluid from the blood and convert this to urine. The urine passes out of the kidney through small tubules into the hollow portion of the kidney (renal pelvis) and then into the ureter, a narrow tube connecting the kidney to the bladder (figure 2). The urine collects in the bladder until it passes out of the body through the urethra.

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 the stone composition is important as this information may guide therapy (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 less than 5 millimeters (0.2 inches) are usually passed without intervention while larger stones usually require treatment.

A kidney stone moves through the urinary tract and, if it is small enough, it will be expelled in the urine. A larger stone may become lodged within the urinary tract, causing pain and sometimes blocking the flow of urine. Occasionally, a stone may not pass into the ureters and can enlarge to fill the entire renal pelvis, which can damage the kidney if it produces infection or obstruction.

KIDNEY STONE SYMPTOMS

The most common symptoms of kidney stones include abdominal or back pain, blood in the urine (hematuria), nausea or vomiting, and the urgent need to urinate. However, some children, particularly young children, do not have any symptoms and the kidney stone is found when an imaging test (eg, x-ray) is done for another reason.

Pain — Pain is the most common symptom of a kidney stone. Pain can range from a mild and barely noticeable ache to intense discomfort. Adolescents are more likely to have pain than young children.

Typically, the pain waxes and wanes in severity. Waves of severe pain, known as renal colic, can last 20 to 60 minutes, although less severe pain can occur between episodes of renal colic.

The area that is painful depends upon the location of the stone, which may change as the stone moves. The most common areas of pain include the flank (one side of the lower back, (figure 3) and the abdomen. Younger children may not be able to say exactly where they feel pain.

Blood in the urine — Hematuria (blood in the urine) occurs in 30 to 50 percent of children with kidney stones. The urine may appear pink or red-colored, or the blood may be visible only when the urine is analyzed in a laboratory. (See "Patient information: Blood in the urine (hematuria) in children".)

Other symptoms — Other common symptoms include nausea or vomiting, pain with urination, and an urgent need to urinate. Pain with urination and an urgent need to urinate can also occur when a child has a urinary tract infection. An evaluation is needed to distinguish between a urinary tract infection and a kidney stone. However, urinary tract infections are often seen in children with kidney stones. (See "Patient information: Urinary tract infections in children".)

KIDNEY STONE RISK FACTORS

Certain factors can increase a child's risk of developing kidney stones.

• 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. Children who have one episode of kidney stones are usually advised to follow preventive measures to decrease the risk of developing a stone in the future. (See 'Kidney stone prevention' below.)

• Low fluid intake — The amount of fluids a child drinks directly affects the amount of urine that is made. Drinking a small amount of fluids means that less urine is made, which increases the concentration of stone-forming substances in the urine. Increasing fluid intake can reduce the risk of recurrent stones. (See 'Increase fluid intake' below.)

• Diet high in animal protein — Children who eat a diet with high levels of animal protein (eg, beef, pork, lamb, chicken) may have an increased risk of developing calcium oxalate stones, especially if the child has difficulties with intestinal absorption. However, normal amounts of protein are essential for growth and do not increase the risk of forming kidney stones.
• Ketogenic diet — Diets that include a very small amount of carbohydrates, called ketogenic diets, can increase the risk of kidney stones. Ketogenic diets are sometimes used to treat seizure disorders. (See "Patient information: Treatment of seizures in children".)

• Cystic fibrosis — Children with cystic fibrosis are at higher risk of developing kidney stones.
• Urinary tract abnormalities — Anatomic abnormalities of the kidneys or ureters, or difficulties with bladder emptying, increase the risk of developing a kidney stone.
• Medications — Some medications promote formation of urine crystals. 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 may be recommended in some cases.

KIDNEY STONE DIAGNOSIS

Urine tests — Two urine tests are recommended for children who are suspected of having a kidney stone. This includes a urine culture, to determine if the child has a urinary tract infection, and a urinalysis, which can determine if microscopic crystals are present in the urine (picture 1). (See "Patient information: Urinary tract infections in children".)

Imaging tests — To confirm the presence of a kidney stone, an imaging test such as a CT scan, ultrasound, or x-ray, is necessary. The imaging test can also help to determine if there are abnormalities of the urinary tract, which would increase the risk for future stones. Computed tomography (CT scan) is the preferred test in most cases.

Computed tomography (CT) scan — A CT scan creates a three dimensional image of structures within the body. A particular type of CT scan (called noncontrast helical CT) can identify almost all types kidney stones (including those that are not seen with the other imaging tests), and can determine if there the stone is blocking (obstructing) the urinary tract (picture 2).

There is some concern about exposing a child to excessive amounts of radiation, especially if the CT scanner uses an adult dose of radiation. In many cases, the amount of radiation can be reduced, based upon the child's size and weight. If this is not possible, another imaging test, such as ultrasound, may be recommended.

Ultrasonography — Ultrasonography (the use of sound waves to visualize body structures) can also be used to detect stones, although small stones and stones in the ureters may be missed. However, ultrasound is the procedure of choice for children who should avoid radiation, such as in pregnant girls or if the dose of radiation in a CT scanner cannot be adjusted for small children.

Abdominal x-ray — Many types of kidney stones can be seen on standard abdominal x-ray (called KUB, kidneys, ureter, bladder). However, certain stones, such as uric acid stones and small stones, may not be seen. As a result, another test, such as a CT scan, may be required if a kidney stone is likely but the abdominal x-ray is negative.

KIDNEY STONE TREATMENT

Treatment at home — If the stone is small, pain is manageable, and the child is otherwise healthy, treatment may be provided at home. Stones smaller than 5 millimeters (0.2 inches) often pass on their own without requiring a procedure, even in young children.

Pain is usually managed with a nonsteroidal antiinflammatory drug such as ibuprofen (Advil®, Motrin®). In addition, the child is encouraged to drink an increased amount of fluids to help flush the stone out of the kidney, ureter, or bladder. (See 'Increase fluid intake' below.)

The parent/child will be asked to strain the child's urine for a few days, until the stone passes. Urine strainers are available from most hospital supply stores, and are placed under the toilet seat. If a urinary strainer cannot be obtained, a receptacle covered by cheese cloth or a fine mesh sheet can be used.

If a stone or stone fragment is passed, it can be analyzed in a laboratory to determine the type; this can help to guide future treatment. Once the stone is passed, an imaging test (usually ultrasound) of the urinary tract may be performed to confirm that the stone was passed and that no fragments or additional stones remain.

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

• The urinary tract is blocked (obstructed) by the stone, preventing the normal flow of urine. If the obstruction 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 and the child's urine will be strained to recover any stone or stone fragments that pass.

However, stones larger than 9 or 10 millimeters (0.4 to 0.45 inches) rarely pass on their own and generally require treatment. Other reasons for treatment include severe pain and obstruction of the urinary tract.

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

Shock wave lithotripsy (SWL) — SWL is the treatment of choice in many children, particularly if the stone is located in the renal pelvis or upper ureter.

To pinpoint the location of the stone, an x-ray or ultrasound is performed. A high-energy shock wave is then directed toward the stone; this passes through the skin and body tissues and causes a release of energy at the stone surface. This energy causes the stone to break into fragments that can be passed. The procedure takes about 20 minutes. Some, although not all, children will require anesthesia to prevent movement during the treatment.

Shock wave lithotripsy (SWL) has been shown to be an effective and safe procedure for removing stones in children, including small children and infants. In one study, the overall percentage of children who had no remaining stones after SWL was 73 percent [1]. The success of the procedure depends, in part, upon the size of the stone; larger stones are more difficult to break up and may require more than one treatment. It may take three months for all of the stone fragments to pass.

Percutaneous nephrolithotomy (PN) — Large stones or stones resistant to shock wave lithotripsy may require a minimally invasive surgical procedure to remove the stone, during which the child is given anesthesia to induce sleep and prevent pain. During the procedure, small telescopic instruments are passed through the skin (percutaneously) into the kidney to remove the stone. This procedure may be combined with shock wave lithotripsy.

The percentage of children who have no remaining stones after PN is between 70 and 90 percent, depending upon the experience of the clinician, the size of the stones, and the presence of an underlying abnormality in the kidney, ureter, or bladder.

Ureteroscopy — Ureteroscopy is often used to remove stones obstructing the middle and lower portion of the ureter. Before the procedure, the child is given anesthesia to induce sleep and prevent pain. A small telescopic instrument is passed through the urethra and bladder, into the ureter and kidney. The telescope contains a camera and other instruments, which allows the physician to see the obstructing stone and remove it or to break the stone up into smaller pieces that can pass more easily.

The percentage of children who have no remaining stones after ureteroscopy is approximately 90 percent.

Prognosis — There are inadequate data about the long term prognosis of children who develop kidney stones. The chances of future kidney stones, kidney damage, and other complications depends largely upon the child's age during the first episode of kidney stones 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 [2]. However, a number of steps can decrease the chance that another stone will develop.

Testing

Blood and urine — After a child has had a kidney stone, blood and urine tests are performed to identify metabolic disorders or other factors that can increase the risk of future stone formation. 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. Urine testing may require the child/parent to collect the urine for 24 hours. (See "Patient information: Collection of a 24-hour urine specimen".)

If it is not possible to collect a 24-hour urine specimen because the child is not toilet trained, a single urine sample may be collected instead. In this case, the urine is collected with a bag that is gently adhered around the child's genitals.

Stone testing — If the stone was passed and saved, it should be analyzed to determine the type of stone. Based upon analysis of the stone, one or more interventions may be recommended to reduce the risk of future stone formation (see 'Interventions' below.

Increase fluid intake — 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.

The volumes recommended below represent the amount of urine a child should make per day, depending upon their age. The child's fluid intake should be increased if he or she makes less than this amount of urine per 24 hours.

• Infants — ≥750 mL (>25 ounces or 3 cups)
• Children younger than five years of age — ≥1000 mL (>33 ounces or 4 cups)
• Children between five and ten years of age — ≥1500 mL (>50 ounces or 6 cups)
• Children greater than 10 years of age — ≥2000 mL (>66 ounces or 8 cups)

Interventions — One or more interventions may be recommended to decrease the concentration of stone-promoting substances in the urine.

Hypercalciuria — Children with increased levels of calcium in the urine may be advised to increase fluid intake and follow these dietary measures:

• Eat a low-sodium diet (graph 1 and table 1) (see "Patient information: Low sodium diet".
• The amount of dietary calcium recommended per day depends upon the child's age: 500 mg/day for children 1 to 3 years, 800 mg/day for children 4 to 8 years, and 1300 mg/day for children 9 years and older. The amount of calcium in selected foods is provided in table 1 (table 2). Consuming excessive amounts of dietary calcium is not recommended. On the other hand, limiting dietary calcium is not recommended because of the importance of calcium in building strong bones.
• Avoid calcium and vitamin D supplements.
• Eat an increased amount of potassium-rich foods, available in most fresh fruits and vegetables.
• If urine calcium levels are not decreased after three to six months of dietary changes, a medication may be recommended.

Hyperoxaluria — Children who have high levels of oxalate in the urine are advised to increase fluids and 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. In addition, vitamin C supplements are not recommended.

Hyperuricosuria — Children with increased levels of urate in the urine are advised to increase fluids and may be given a treatment to increase the pH of the urine (potassium citrate or potassium carbonate).

Cystinuria — Children with high levels of cystine in the urine are encouraged to increase fluid intake and may be given a medication that reduces the acidity (ie, increases the pH) of the urine (potassium citrate or potassium carbonate). To ensure that fluid intake is adequate and that the urine pH is alkaline (the opposite of acidic), a urine sample may be tested.

Hypocitraturia — 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 as a result of urinary tract infections. Efforts to prevent recurrent struvite stones include prevention of urinary tract infections. This is discussed in detail in a separate topic review. (See "Patient information: Urinary tract infections in children".)

Complementary and alternative therapies — There are no data on the efficacy and safety of complementary and alternate therapies in the treatment of kidney stones in children. Nevertheless, both herbal and acupuncture therapies have commanded widespread interest and use, especially in Asian countries. We do not recommend these therapies as they remain unproven.

Monitoring — Following the first episode of kidney stones, imaging tests may be recommended to monitor for the development of new stones, especially in children who have multiple risk factors. The most common test used for monitoring is ultrasound. The frequency of monitoring depends upon the type and number of stones during the first episode, and the presence and severity of any underlying metabolic abnormality.

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. Because no two children are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your child's situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Kidney stones in adults
Patient information: Blood in the urine (hematuria) in children
Patient information: Urinary tract infections in children
Patient information: Treatment of seizures in children
Patient information: Collection of a 24-hour urine specimen
Patient information: Low sodium diet

Professional Level Information:
Acute management of nephrolithiasis in children
Clinical features and diagnosis of nephrolithiasis in children
Epidemiology of and risk factors for nephrolithiasis in children
Prevention of recurrent nephrolithiasis in children

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

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

• The Centers for Disease Control and Prevention

      (www.cdc.gov/)

• National Institute of Diabetes and Digestive and Kidney Diseases

      (www.niddk.nih.gov)

• The American Academy of Pediatrics

      (www.aap.org)

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