Uric acid stones form in the urinary tract when certain conditions are present. Identifying the risk factors can help guide management.



(1) uric acid

(2) uric acid dihydrate (requires very low urine pH)


The pK for uric acid and urate. If the urine pH is < 5.5 then more uric acid is formed. Uric acid is much less soluble than urate.


Risk factors:

(1) older age (often > 60 years)

(2) male gender

(3) obesity, often with glucose intolerance or diabetes

(4) diet rich in purines, proteins and alcohol

(5) gout with hyperuricemia

(6) low urine pH from a high acid load or decreased alkali

(7) dehydration


Imaging studies:

(1) X-ray: radiolucent

(2) ultrasonography: high density and typical echo

(3) spiral CT: visible


Urine findings in uric acid stones:

(1) acid pH (< 6.0, often < 5.5)

(2) usually an increased concentration of uric acid (hyperuricosuria), with uric acid >= 4.0 mmol per 24 hours

(3) uric acid crystals in the urine sediment

(4) stone analysis shows increased uric acid


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