Use of the excreted fraction of the filtered sodium (Fe Na) in the early diagnosis of acute renal failure.

A prospective study was made in 20 patients in the oliguric phase of acute renal failure, 20 patients with prerenal uremia (functional renal failure); 20 patients hospitalized due to different diseases but without renal problems and 20 healthy individuals. In all patients osmolar clearance, free water clearance, urinary sodium and excreted fraction of sodium tests were made. These four parameters could differentiate acute renal failure from prerenal uremia. However differences in urinary sodium concentrations in patients with prerenal uremia was found to be in the borderline for statistical significance and osmolar and free water clearance determinations require strict measurements of urinary volume in a time unit. Excreted sodium fraction requires only simultaneous blood and urine samples for sodium and creatinine quantification.