Uric Acid Stones Treatment & Management

The primary treatments are to alkalinize (citrate or bicarbonate) and dilute (large water intake) the urine. Sodium urate is 15 times more soluble than uric acid. At a urine pH level of 6.8, 10 times as much sodium urate as uric acid is present. At a urine pH level of 7.8, 100 times as much urate as uric acid is present.

A systematic review showed that complete or partial dissolution of uric acid stones was achieved in 80.5% of patients who received medical therapy; of those patients, 61.7% had complete and 19.8% had partial dissolution. ^[14]  A study by Nevo et al, in which complete and partial dissolution of uric acid stones occurred in 33% and 22% of patients, respectively, demonstrated that successful medical therapy is more cost-effective than surgical management. ^[15]

Children with uric acid stones tend to have 1 of 3 types of presentations: (1) renal colic, gross hematuria, and infection; (2) renal colic with or without hematuria with one or more large stones or renal colic with or without hematuria with one or more small stones; and (3) one or more stones found incidentally.

• A child with severe acute pain and the likelihood of infection should be admitted to the hospital. Pain should be managed with analgesics and narcotics if necessary. A urine Gram stain may guide in the selection of antibiotic coverage. Consultation with a pediatric urologist should be obtained because surgery may be necessary to provide drainage.

• A child with acute pain and large stones (>0.3 cm) is likely to require lithotripsy or surgical stone removal. Analgesics and adequate hydration should be provided.

• For smaller stones or incidental stones, allowing time for the stone to pass is appropriate. The primary treatment for uric acid stones includes increased hydration (urine output increased to 30 mL/kg/24h) and alkalinization (urine pH level >7) of the urine. If uric acid overproduction is the problem, allopurinol may be indicated. In Lesch-Nyhan syndrome, uric acid stones may respond to hydration and urine alkalinization. ^[16] If increased urinary uric acid concentration is secondary to medication, substitution to another agent that is less uricosuric is suggested.

• In an infant or child with acute renal failure secondary to uric acid crystals, allopurinol and dialysis may be indicated in addition to supportive care for renal failure.

• Most children with uric acid calculi do not have hyperuricemia. Elevated serum uric acid levels are frequently due to dehydration and excessive purine intake. Consistently low urine pH is a risk factor for stone formation. As the urine pH level increases above the pK (5.8), uric acid forms the more soluble urate ion.

• Children with uric acid stones frequently describe passing gravel. With persistent urinary alkalinization and large urine output, urinary uric acid stones can dissolve with time.

Surgical treatments may include ureteroscopic stone extraction, percutaneous nephrolithotomy, open stone surgery, and extracorporal shock wave lithotripsy.

Stones may need to be removed by a pediatric urologist. The technique used depends on stone size and location.

The diagnosis of uric acid stones in a child mandates consultation with a pediatric nephrologist and urologist.

• Consulting a pediatric nephrologist is necessary to perform a metabolic evaluation and provide follow-up care for children with uric acid nephropathy or uric acid stones.

• Consultation with a pediatric urologist may be necessary for removal of uric acid stones.

Diet

Hydration is one of the most important dietary issues. The child should be encouraged to drink enough water to maintain a urine output of 30 mL/kg/d. ^[7]  The urine should be collected and measured until the quantity of water needed each day is understood. Most children have nocturia on this regimen. Water intake may need to be greater in the summer and in warm climates.

A diet low in purine (ie, limited quantities of liver, kidney, brains, sweetbreads, fish, poultry, asparagus, spinach, peas, and beans) may aid in lowering the total-body burden of uric acid and other purine metabolites. Children do not generally have problems with limiting the above items.

Activity

No change in activity is necessary.

Further outpatient care

The child should continue a low-purine diet if prescribed.

• Continue Bicitra (2-6 mEq/kg/d) for urinary alkalinization.

• Parents can be provided urine dipsticks to monitor urine pH level and specific gravity to assess the adequacy of treatment. Urine pH levels should be maintained above 7. Urine specific gravity should be maintained below 1.01.

• Fluid intake should be sufficient to maintain urine output of 30 mL/kg/24h or more.

• Allopurinol is continued to lower uric acid production if prescribed.

Children with urinary tract uric acid stones and/or urinary tract anatomic abnormalities or a previous urinary tract infection may require urinary tract infection uroprophylaxis.

A low-purine diet, allopurinol, Bicitra, and aggressive hydration should be continued. The goals are to dissolve present stones and to prevent new stones.

Further inpatient care

Inpatient care is indicated for management of renal failure, urologic surgery, severe pain, infection, or obstruction.

Prevention

A low-purine diet, urinary alkalinization, and large fluid intake may prevent new stones from forming.