FRACTIONAL EXCRETION OF SODIUM

FRACTIONAL EXCRETION OF SODIUM (FENA) IS THE FRACTION OF FILTERED SODIUM LOAD THAT IS REABSORBED BY THE TUBULES AND IS A MEASURE OF BOTH THE KIDNEYS ABILITY TO REABSORB SODIUM AS WELL AS ENDOGENOUS AND EXOGENOUS FACTORS THAT AFFECT TUBULAR REABSORPTION. WITH PRERENAL AZOTEMIA, FENA IS USUALLY <1% SUGGESTING AVID TUBULAR SODIUM REABSORPTION. LOW FENA IS OFTEN SEEN IN GLOMERULONEPHRITIS, HENCE SHOULD NOT BE CONSIDERED SYNONYMOUS WITH INTRAVASCULAR VOLUME DEPLETION AND SHOULD NOT BE USED AS A SOLE GUIDE FOR VOLUME MANAGEMENT. IN ISCHEMIC AKI, FENA IS FREQUENTLY >1% BECAUSE OF TUBULAR INJURY AND RESULTANT INABILITY TO REABSORB SODIUM.