Which statement correctly pairs AKI type with typical FeNa?

• A. Prerenal AKI: FeNa <1%; Intrinsic AKI: FeNa >2%.
• B. Prerenal AKI: FeNa <1%; Intrinsic AKI: FeNa >2%.
• C. Prerenal AKI: FeNa <1%; Intrinsic AKI: FeNa <1%.
• D. Prerenal AKI: FeNa >2%; Intrinsic AKI: FeNa >2%.

Answer: (A)

FeNa, or fractional excretion of sodium, helps differentiate prerenal AKI from intrinsic AKI by reflecting how the kidney handles sodium when perfusion changes. In prerenal AKI, reduced renal blood flow prompts the kidney to conserve sodium, so the FeNa stays very low, typically less than 1%. In intrinsic AKI, such as acute tubular necrosis, tubular injury impairs sodium reabsorption, leading to more sodium loss in the urine and a FeNa usually greater than 2%. This pattern—FeNa <1% for prerenal and FeNa >2% for intrinsic—best matches the underlying physiology. Note that diuretics can blur this distinction, in which case alternative measures like FeUrea may be helpful.