In patients undergoing kidney evaluation, how is the fractional excretion of sodium typically interpreted?

The fractional excretion of sodium (FENa) is a valuable tool in assessing renal function, particularly in the context of acute kidney injury (AKI). It measures the percentage of filtered sodium that is excreted in the urine. A high FENa value typically indicates that the kidneys are unable to adequately reabsorb sodium, which is often seen in conditions such as acute tubular necrosis (ATN). In contrast, a low FENa value suggests that the kidneys are appropriately reabsorbing sodium, a response often seen in prerenal azotemia, where the kidneys are trying to conserve sodium due to low blood volume or reduced perfusion.

By interpreting FENa in this way, healthcare providers can differentiate between prerenal and intrinsic renal causes of kidney injury, which is critical for determining the appropriate management and treatment of the underlying condition. Hence, the correct interpretation of FENa as an indicator of renal function through sodium reabsorption provides essential information regarding the status of the kidneys in patients undergoing evaluation for renal issues.