What sign might indicate renal hypoperfusion in heart failure?

• A. Increased urine output
• B. Decreased urine output with rising BUN/creatinine; prerenal azotemia
• C. Normal renal function
• D. Hyperkalemia

Answer: (B)

When the heart isn’t pumping effectively, the kidneys don’t get enough blood (renal hypoperfusion). In response, the kidneys try to conserve volume, which reduces urine production and increases reabsorption of urea. This causes a rise in BUN that outpaces the rise in creatinine, leading to a higher BUN/creatinine ratio and oliguria. This pattern—decreased urine output with rising BUN and creatinine—best signals prerenal azotemia from reduced renal perfusion due to heart failure.

Increased urine output wouldn’t indicate poor perfusion, normal renal function suggests perfusion is adequate, and hyperkalemia isn’t a specific sign of renal hypoperfusion from heart failure (it can occur with other renal or metabolic problems).