Which finding supports a prerenal cause of acute kidney injury?

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Multiple Choice

Which finding supports a prerenal cause of acute kidney injury?

The key idea is using urine indices to distinguish prerenal AKI from intrinsic kidney injury. In prerenal AKI, reduced renal perfusion prompts the kidneys to conserve sodium aggressively to maintain intravascular volume. This results in very low sodium in the urine, commonly less than 20 mEq/L, and a fractional excretion of sodium (FE Na) under 1%. Because of this sodium avidity, a low urine sodium concentration is the strongest clue pointing to a prerenal cause. In contrast, if the kidney tubules are damaged or overwhelmed, they lose the ability to reclaim sodium, leading to higher urine sodium and FE Na. Normal urine sodium is not supportive of prerenal, and high urine sodium makes a prerenal diagnosis unlikely. Keep in mind diuretic use can raise urine sodium even when prerenal physiology is present, which can blur the picture.

The key idea is using urine indices to distinguish prerenal AKI from intrinsic kidney injury. In prerenal AKI, reduced renal perfusion prompts the kidneys to conserve sodium aggressively to maintain intravascular volume. This results in very low sodium in the urine, commonly less than 20 mEq/L, and a fractional excretion of sodium (FE Na) under 1%. Because of this sodium avidity, a low urine sodium concentration is the strongest clue pointing to a prerenal cause.

In contrast, if the kidney tubules are damaged or overwhelmed, they lose the ability to reclaim sodium, leading to higher urine sodium and FE Na. Normal urine sodium is not supportive of prerenal, and high urine sodium makes a prerenal diagnosis unlikely. Keep in mind diuretic use can raise urine sodium even when prerenal physiology is present, which can blur the picture.

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