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
