Although the fractional excretion of
uric acid (FEUA) is known to reflect extracellular fluid volume changes, the diagnostic significance of decreased FEUA in
dehydration has not been previously reported. We studied the possible association between low FEUA and acute prerenal
azotemia, and its diagnostic value, compared with other traditional indices, in discriminating prerenal
azotemia from renal parenchymal causes of
acute renal failure. In 65
chronic renal disease patients, 174 FEUA measurements were obtained from 24-hour urine collections. FEUA levels increased as reciprocal serum
creatinine levels decreased. All 8 patients with prerenal
azotemia showed significantly decreased FEUA values compared with
chronic renal disease patients with a comparable degree of serum
creatinine elevation, whereas all 7 patients with
acute renal failure had FEUA values higher than those of
chronic renal disease patients with comparable
creatinine levels. FEUA values in prerenal
azotemia were distinctly lower than those in
acute renal failure (p less than 0.001). Patients with prerenal
azotemia showed a lower fractional excretion of
sodium, a lower fractional excretion of
chloride and
renal failure index, and a higher urine-to-plasma
creatinine ratio than those with
acute renal failure (p less than 0.05). However, these traditional indices were not useful in discriminating between the two conditions. The urine-to-plasma
urea nitrogen ratio and the ratio of plasma
urea nitrogen to
creatinine showed no statistical difference between prerenal
azotemia and
acute renal failure. We conclude that, in acute
azotemia, a decreased FEUA value may represent a reliable
indicator of prerenal
azotemia in the differential diagnosis of
acute renal failure.