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Kidney Stones

The kidney eliminates excess water, salts (like sodium, potassium, and chloride), and minerals (like calcium and phosphate) from the body.  Sometimes these minerals will form crystals in the urine that can come together to form a hard deposit or stone.  Kidney stones are relatively uncommon in children though the number of cases has been increasing. 


When these stones are located in the kidney they rarely cause symptoms.  However, as a stone moves, if it blocks the flow of urine (either in the kidney or the ureter, the tube connecting the kidney to the bladder) it can cause intense pain.  The pain is often described as “renal colic” as the pain and associated severe nausea comes in waves.  The pain often begins in the upper back (or flank) and moves down and forward to the abdomen and then groin.  Sometimes patients will have blood visible in the urine.

When to Seek Emergency Care

Fortunately, most kidney stones (even large ones) pass through the urinary tract on their own, and as they reach the bladder the pain resolves.  However, if the pain is not improving it is important that your child be seen in an emergency department Either kidney ultrasound or CT scan may be done to find the size and location of the stone.  Sometimes medication to help the stone pass can be prescribed.  If necessary, referral to urology can be generated.  Depending upon the circumstance, urology may prefer to monitor for days or longer, as again, most stones pass by themselves.  However,

After a stone has passed or after urology has performed surgery, a child may be referred for evaluation by a pediatric nephrologist.  The purpose of this evaluation is to make certain the child does not have one of the rare inherited or metabolic abnormalities that can cause kidney stones and to prescribe diet measures (or more rarely medication) that can decrease the risk of developing kidney stones again in the future.

Lab Analysis of Stone

If your child passes a stone you should try to keep it. The stone can be placed in a plastic zip lock bag and brought to a lab for analysis. Most kidney stones are made of calcium oxalate or calcium phosphate, but there are many more unusual type of stones; there are certain dietary measures suggested no matter the type of stone, but other diet advice will differ depending upon the type of stone. If the stone is not available for testing your child may be asked to collect urine for a 24 hour period. Analysis of this type of collection can help diagnose the factor predisposing your child to developing kidney stones. In addition, a blood test is generally done to assess rare hormonal or metabolic problems that can cause kidney stones.

Increase Water Consumption

All children who have had a kidney stone are instructed to drink more water. Increased water drinking increases the amount of water in the urine (making the urine clear rather than yellow) and dilute the minerals in urine so they cannot form crystals.  Teenagers are usually advised to drink 2-3 liters or more of water per day – this is 70-100 ounces.  Drinking water before bed and then getting up at night to void and drink is most effective.  Of note, other liquids like dark sodas (phosphates), tea (oxalates), and sports drinks (sodium), have substances that can increase the risk of developing kidney stones.  One liquid that can often help prevent stones is lemonade (made with real lemon juice).  Lemons have a natural body substance (citrate) that is eliminated in the urine and prevents mineral salts from crystallizing. 

Diet Measures

Most children who have had a kidney stone are advised to limit sodium (or salt) intake.  Increased sodium in the diet forces the kidney to increase the sodium in urine.  In turn, sodium drags calcium and other substances that form kidney stones into the urine.  Most teenagers are advised a diet with 2500 mg or less of sodium per day; many phone apps can be downloaded that detail the sodium content of most foods.  We advise families use one of these tools to evaluate the sodium content of their child’s typical diet and gain insight into areas that require change. 

Other diet measures that may be prescribed include moderation in consumption of animal protein; animal proteins are metabolized in the body to uric acid which is eliminated by the kidney and can increase the risk of uric acid stones and calcium containing stones.  In general, limiting daily intake of red meat, poultry, or seafood to the size of a pack of cards per day is helpful.  As noted previously the most common type of kidney stone is calcium oxalate.  Oxalate is a natural body substance that is also found in many plant foods and is eliminated in the kidney.  Fortunately, most foods very high in oxalate are not common in most person’s diet (such as spinach, rhubarb, tea, and most nuts).  There are phone apps that can be downloaded that detail the oxalate content of most foods and goal for persons with kidney stones is an intake less than 100 mg per day.

Lastly, it is important to emphasize that restricting the amount of calcium in the diet does NOT decrease the risk of kidney stones.  Calcium is obviously important for normal bone development and should be consumed generously in almost all situations.

For more information regarding diet measures in persons predisposed to kidney stones, visit the NIH's web page on Diet for Kidney Stone Prevention.