Neonatal renal failure: usefulness of diagnostic indices.

Forty-two oliguric neonates were prospectively studied to evaluate the usefulness and reliability of various diagnostic indices in differentiating renal failure from functional (prerenal) oliguria. Twenty-two infants had functional oliguria, 16 had renal failure, and four infants had probable early renal failure. Statistically significant differences between functional oliguria and renal failure were found with regard to the urine sodium, urine to serum ratios of sodium, urea, and creatinine, renal failure index, and fractional excretion of sodium. However, sharp demarcation of the two groups was possible only when the renal failure index or fractional excretion of sodium was used. Fractional excretion of sodium values of 2.5 or greater seem to differentiate renal failure from functional oliguria in this study.