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Uric acid nephrolithiasis

INTRODUCTION

Uric acid stones are nonopaque on radiologic examination [1,2]. The prevalence of uric acid stones among patients with gout prior to effective antihyperuricemic treatment was about 20 percent, several hundred-fold greater than that in the adult nongouty population.

Uric acid stones account for only 5 to 10 percent of all urinary tract stones in the United States and Europe. However, they comprise 40 percent or more of stones in areas with hot, arid climates in which the tendency to a low urine volume and acid urine pH promote uric acid precipitation.

More than 80 percent of uric acid stones in patients with gout are composed entirely of uric acid. The remainder contain calcium oxalate or calcium phosphate surrounding a central nidus of uric acid. The prevalence of calcium oxalate stones among patients with gout is 10- to 30-fold that of individuals without gout. This may be due to increased urinary calcium excretion and decreased citrate excretion [3]. (See "Risk factors for calcium stones in adults".)

This topic provides an overview of the diagnosis and treatment of uric acid stone disease. The general approach to the patient with nephrolithiasis and other management issues related to hyperuricemia and gout are discussed separately. (See "Diagnosis and acute management of suspected nephrolithiasis in adults" and "Evaluation of the adult patient with established nephrolithiasis and treatment if stone composition is unknown" and "Clinical manifestations and diagnosis of gout" and "Asymptomatic hyperuricemia".)

RISK FACTORS

Uric acid nephrolithiasis primarily occurs in patients with no obvious abnormality in uric acid metabolism. However, upon closer examination, many possess a combination of findings that together favor stone formation. These include relatively high serum uric acid levels, comparatively low urinary pH, and low fractional excretion of urate [4-6]. These abnormalities are similar to those seen in most patients with primary gout (underexcretors). (See "Asymptomatic hyperuricemia".)
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References Top
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