Which scenario is most likely to cause prerenal acute kidney injury?

• A. Volume depletion (vomiting, diarrhea)
• B. Acute tubular necrosis due to nephrotoxin
• C. Postrenal obstruction due to stones
• D. Renal artery stenosis

Answer: (A)

Prerenal AKI occurs when kidney perfusion drops, so the kidneys receive less blood flow and filtration falls even though the kidney tissue itself is initially intact. Loss of fluids from vomiting and diarrhea reduces the circulating blood volume, lowering effective arterial blood volume and renal perfusion. In response, the kidneys conserve water and sodium through mechanisms like RAAS activation, which helps maintain blood pressure and GFR, but also leads to a concentrated urine with low sodium content. This perfusion problem is the classic setup for prerenal AKI because it is reversible if the volume deficit is corrected.

In this scenario, volume loss from GI symptoms is the most likely trigger because it directly reduces circulating volume and renal blood flow. By contrast, acute tubular necrosis from a nephrotoxin represents intrinsic kidney injury where the tubules themselves are damaged; postrenal obstruction from stones causes AKI due to impaired urine outflow and increased tubular pressure rather than reduced perfusion; renal artery stenosis lowers renal perfusion chronically but is not the immediate cause in a simple volume-depletion context.