In prerenal acute kidney injury, which of the following best describes the typical BUN: Creatinine ratio and urine sodium?

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Multiple Choice

In prerenal acute kidney injury, which of the following best describes the typical BUN: Creatinine ratio and urine sodium?

Explanation:
In prerenal AKI, reduced kidney perfusion triggers mechanisms that conserve sodium and water. This causes more urea to be reabsorbed, so the BUN rises relative to creatinine, giving a BUN:creatinine ratio often greater than 20:1. The kidney also reabsorbs sodium avidly to preserve volume, so urine sodium is low (usually <20 mEq/L). The fractional excretion of sodium stays low as well (FeNa <1%), reflecting intact tubular reabsorption rather than tubular damage. This pattern helps distinguish prerenal from intrinsic renal injury (like ATN), where BUN:Cr is typically not elevated relative to creatinine, urine sodium is higher (>40 mEq/L), and FeNa is >2%. So the typical description for prerenal AKI is BUN:Cr >20:1, urine Na <20 mEq/L, and FeNa <1%.

In prerenal AKI, reduced kidney perfusion triggers mechanisms that conserve sodium and water. This causes more urea to be reabsorbed, so the BUN rises relative to creatinine, giving a BUN:creatinine ratio often greater than 20:1. The kidney also reabsorbs sodium avidly to preserve volume, so urine sodium is low (usually <20 mEq/L). The fractional excretion of sodium stays low as well (FeNa <1%), reflecting intact tubular reabsorption rather than tubular damage.

This pattern helps distinguish prerenal from intrinsic renal injury (like ATN), where BUN:Cr is typically not elevated relative to creatinine, urine sodium is higher (>40 mEq/L), and FeNa is >2%.

So the typical description for prerenal AKI is BUN:Cr >20:1, urine Na <20 mEq/L, and FeNa <1%.

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