What is a kidney stone?
A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated. A stone may stay in the kidney or travel down the urinary tract. From smaller pieces to large stones, kidney stones vary in size.
A small stone may pass out of the body causing little or no pain. A larger stone may get stuck along the urinary tract and can block the flow of urine, causing severe pain or blood that can be seen in the urine.
What is the urinary tract?
The urinary tract is the body’s drainage system for removing wastes and extra water. The urinary tract includes two kidneys, two ureters, a bladder, and a urethra. The kidneys are a pair of bean-shaped organs, each about the size of a fist and located below the ribs, one on each side of the spine, toward the middle of the back.
Every minute, a per- son’s kidneys filter about 3 ounces of blood, removing wastes and extra water. The wastes and extra water make up the 1 to 2 quarts of urine an adult produces each day. Children produce less urine each day; the amount produced depends on their age. The urine travels from the kidneys down two narrow tubes called the ureters. The urine is then stored in a balloon-like organ called the bladder. When the bladder empties, urine flows out of the body through a tube called the urethra at the bottom of the bladder.
Are kidney stones common in children?
No exact information about the incidence of kidney stones in children is available, but many kidney specialists report seeing more children with this condition in recent years.
While kidney stones are more common in adults, they do occur in infants, children, and teenagers from all races and ethnicities.
What causes kidney stones in children?
Kidney stones can form when substances in the urine—such as calcium, magnesium, oxalate, and phosphorous—become highly concentrated due to one or more causes:
Defects in the urinary tract may block the flow of urine and create pools of urine.
In stagnant urine, stone-forming substances tend to settle together into stones. Up to one-third of children who have stones have an anatomic abnormality in their urinary tract.
Kidney stones may have a genetic cause.
In other words, the tendency to form stones can run in families due to inherited risk factors.
An unhealthy lifestyle may make children more likely to have kidney stones.
For example, drinking too little water or drinking the wrong types of fluids, such as soft drinks or drinks with caffeine, may cause substances in the urine to become too concentrated. Similarly, too much sodium, or salt, in the diet may contribute to more chemicals in the urine, causing an increase in stone formation. Some doctors believe increases in obesity rates, less active lifestyles, and diets higher in salt may be causing more children to have kidney stones.
Sometimes, a urinary tract infection can cause kidney stones to form.
Some types of bacteria in the urinary tract break down urea—a waste product removed from the blood by the kidneys—into substances that form stones.
Some children have metabolic disorders that lead to kidney stones.
Metabolism is the way the body uses digested food for energy, including the process of breaking down food, using food nutrients in the body, and removing the wastes that remain. Hypercalciuria, or excessive urinary calcium excretion, is the most common identifiable cause of calcium kidney stone disease.
Other more rare metabolic conditions involve problems breaking down oxalate, a substance made in the body and found in some foods. These conditions include hyperoxaluria, too much oxalate in the urine, and oxalosis, characterized by deposits of oxalate and calcium in the body’s tissues. Another rare metabolic condition called cystinuria can cause kidney stones. Cystinuria is an excess of the amino acid cystine in the urine. Amino acids are the building blocks of proteins.
What are the signs and symptoms of kidney stones in children?
Children with kidney stones may have pain while urinating, see blood in the urine, or feel a sharp pain in the back or lower abdomen. The pain may last for a short or long time. Children may experience nausea and vomiting with the pain. However, children who have small stones that pass easily through the urinary tract may not have symptoms at all.
What types of kidney stones occur in children?
Four major types of kidney stones occur in children:
Calcium stones are the most common type of kidney stone and occur in two major forms:
Calcium oxalate and calcium phosphate. These are more common. Calcium oxalate stone formation has various causes, which may include high calcium excretion, high oxalate excretion, or acidic urine. Calcium phosphate stones are caused by alkaline urine.
Uric acid stones form when the urine is persistently acidic.
A diet rich in purines—substances found in animal proteins such as meats, fish, and shellfish—may cause uric acid. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium.
Struvite stones result from kidney infections.
Eliminating infected stones from the urinary tract and staying infection-free can prevent more struvite stones.
Cystine stones
These result from a genetic disorder that causes cystine to leak through the kidneys and into the urine in high concentration, forming crystals that tend to accumulate into stones.
How are kidney stones in children prevented?
To prevent kidney stones, health care providers and their patients must understand what is causing the stones to form. Especially in children with suspected metabolic abnormalities or with recurrent stones, a 24-hour urine collection is obtained to measure daily urine volume and to determine if any underlying mineral abnormality is making a child more likely to form stones. Based on the analysis of the collected urine, the treatment can be individualized to address a metabolic problem.
In all circumstances, children should drink plenty of fluids to keep the urine diluted and flush away substances that could form kidney stones. Urine should be almost clear.
Points to Remember
A kidney stone is a solid piece of material that forms in a kidney when some substances that are normally found in the urine become highly concentrated.
- Kidney stones occur in infants, children, and teenagers from all races and ethnicities.
- Kidney stones in children are diagnosed using a combination of urine, blood, and imaging tests.
- The treatment for a kidney stone usually depends on its size and composition as well as whether it is causing symptoms of pain or obstructing the urinary tract.
- Small stones usually pass through the urinary tract without treatment. Still, children will often require pain control and encouragement to drink lots of fluids to help move the stone along.
- Children with larger stones, or stones that block urine flow and cause great pain, may need to be hospitalized for more urgent treatment.
- Hospital treatments may include shock wave lithotripsy (SWL), removal of the stone with a ureteroscope, lithotripsy with a ureteroscope, or percutaneous nephrolithotomy.
- To prevent recurrent kidney stones, health care providers and their patients must understand what is causing the stones to form.
- In all circumstances, children should drink plenty of fluids to keep the urine diluted and flush away substances that could form kidney stones. Urine should be almost clear.
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