[Serum uric acid level and fractional excretion of urate in fluid and electrolyte disturbances].

Changes in renal urate clearance may reflect altered glomerular dynamics more precisely than other commonly used indices. Extracellular fluid volume expansion is known to be correlated with uricosuria, while volume depletion is associated with decreased urate excretion. The diagnostic usefulness of measuring serum urate levels and fractional excretions of urate in SIADH, incipient diabetic nephropathy, and prerenal azotemia have been reviewed. In SIADH, profound hypouricemia and markedly increased fractional excretion of urate (FEUA) accompany the extracellular fluid volume expansion. In prerenal azotemia, decreased FEUA may represent a reliable indicator of prerenal azotemia in the differential diagnosis of acute renal failure. In incipient diabetic nephropathy, glomerular hyperfiltration may increase renal urate clearance and lower the serum uric acid level. Hypouricemia may also predict the future progression of incipient nephropathy in type II diabetes.