What can limit the use of fractional excretion of sodium (FeNa) in diagnostics?

The fractional excretion of sodium (FeNa) is a valuable diagnostic tool used to differentiate between prerenal and intrinsic renal causes of acute kidney injury (AKI). However, its reliability can be significantly affected by various factors, and one of the most impactful is diuretic use.

When diuretics are administered, they increase urine flow by promoting sodium excretion. This results in a lowered concentration of sodium in the urine as the kidneys actively adjust to maintain sodium balance; thus, the fractional excretion of sodium may not accurately reflect the kidney’s ability to reabsorb sodium. In cases where diuretics are used, patients may display an artificially high FeNa value due to increased urine output and sodium excretion, which can lead to misinterpretation of kidney function and potentially incorrect clinical decisions.

Understanding the effects of diuretic therapy is crucial since it can obscure the true physiological status of the kidneys. Therefore, while FeNa is a useful metric, its interpretation must consider whether the patient is on diuretics to avoid misleading conclusions regarding their renal function.