Fractional Excretion of Sodium
The fractional excretion of sodium (FeNa) calculation predicts the likelihood that a patient with acute renal failure has acute tubular necrosis (ATN). In ATN, the kidneys have difficulty reabsorbing sodium and concentrating urine. The following formula takes advantage of this by using plasma sodium and creatinine concentrations (P[Na] and P[Cr]) and spot urine sodium and creatinine levels (U[Na] and U[Cr]):FeNa = (U[Na] × P[Cr])/(P[Na] × U[Cr]) × 100
FeNa > 2% suggests post-glomerular failure
FeNa < 1% suggests prerenal azotemia (volume depletion).
The fractional excretion of sodium (FeNa) calculation predicts the likelihood that a patient with acute renal failure has acute tubular necrosis (ATN). In ATN, the kidneys have difficulty reabsorbing sodium and concentrating urine. The following formula takes advantage of this by using plasma sodium and creatinine concentrations (P[Na] and P[Cr]) and spot urine sodium and creatinine levels (U[Na] and U[Cr]):FeNa = (U[Na] × P[Cr])/(P[Na] × U[Cr]) × 100
FeNa > 2% suggests post-glomerular failure
FeNa < 1% suggests prerenal azotemia (volume depletion).