Asymptomatic hyperuricemia

INTRODUCTION

Asymptomatic hyperuricemia is the term applied to settings in which the serum urate concentration is elevated, but neither symptoms nor signs of urate crystal deposition (gout) have occurred. Although gout may develop in a hyperuricemic individual at any point, it is likely that two-thirds or more of hyperuricemic individuals will remain asymptomatic [1-5]. The implications of hyperuricemia may be broadly regarded as those related to urate or uric acid crystal deposition and those emerging from crystal deposition-unrelated associations of hyperuricemia with important disorders, including hypertension, chronic kidney disease, cardiovascular disease, and the insulin resistance syndrome.

The etiology and management of asymptomatic hyperuricemia will be reviewed here. Gout, uric acid renal diseases, and uric acid nephrolithiasis are discussed separately. (See "Clinical manifestations and diagnosis of gout" and "Treatment of acute gout" and "Prevention of recurrent gout" and "Uric acid renal diseases" and "Uric acid nephrolithiasis".)

DEFINITIONS

The statistical definition of hyperuricemia is difficult to accept because of non-normal distribution of serum urate concentrations in most populations. For purposes relating to urate crystal deposition, a definition of hyperuricemia based on the solubility limit of urate in body fluids (ie, the concentration at which a state of supersaturation for urate is reached in the serum) is appropriate. This physicochemical definition corresponds to urate concentrations exceeding about 7.0 mg/dL (416 mmol/L), as measured by automated enzymatic (uricase) methods in routine clinical laboratory use. These values are approximately 1 mg/dL (60 mmol/L) lower than those obtained with colorimetric methods.

A definition of hyperuricemia appropriate to the non-crystal deposition-associations of hyperuricemia with the conditions listed above is more problematic for two reasons: first, the high prevalence of urate values exceeding saturation but within 2 standard deviations of the population mean (for example, an estimated 5 to 8 percent in adult white males in the US and 25 percent in Taiwan Chinese males [6]); and second, the fact that associations of serum urate levels with cardiovascular and other disorders are manifested at concentrations that are clearly subsaturating [7].

Classification — Persistent hyperuricemia is a common biochemical abnormality that results from excessive urate production and/or diminished renal uric acid excretion [8]. (See "Uric acid balance".)