In prerenal azotemia, the fractional excretion of sodium (FENa) is typically what value?

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Multiple Choice

In prerenal azotemia, the fractional excretion of sodium (FENa) is typically what value?

In prerenal azotemia, the kidneys respond to reduced renal perfusion by conserving sodium. This means very little sodium is lost in the urine, so the fractional excretion of sodium is very low. The typical value is less than 1%, reflecting intense tubular reabsorption of Na+ to preserve intravascular volume. This contrasts with intrinsic renal failure (like ATN), where damaged tubules fail to reabsorb Na+ efficiently, leading to a higher FENa (often >2%). A value around 1–2% can be seen in some cases and may be less specific, but the classic teaching for prerenal azotemia is FENa <1%. If the patient is on diuretics, FENa can be misleadingly higher, in which case FEUrea can be a more reliable differentiator.

In prerenal azotemia, the kidneys respond to reduced renal perfusion by conserving sodium. This means very little sodium is lost in the urine, so the fractional excretion of sodium is very low. The typical value is less than 1%, reflecting intense tubular reabsorption of Na+ to preserve intravascular volume.

This contrasts with intrinsic renal failure (like ATN), where damaged tubules fail to reabsorb Na+ efficiently, leading to a higher FENa (often >2%). A value around 1–2% can be seen in some cases and may be less specific, but the classic teaching for prerenal azotemia is FENa <1%. If the patient is on diuretics, FENa can be misleadingly higher, in which case FEUrea can be a more reliable differentiator.

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