Oliguria in prerenal AKI is best described as?

• A. Oliguria results from decreased GFR due to reduced perfusion
• B. Oliguria results from urinary obstruction
• C. Oliguria is not related to GFR
• D. Oliguria indicates intrinsic renal damage

Answer: (A)

Oliguria in prerenal AKI happens because kidney blood flow is reduced, which lowers the filtration rate. When perfusion to the kidneys drops, the pressure driving filtration at the glomerulus falls, so GFR decreases and urine output decreases accordingly. This is a problem before the kidneys (pre-renal), and the body’s goal is to maintain GFR by adjusting renal arteriolar tone, but if the hypoperfusion continues, the filtration rate—and thus urine production—remains low. If the underlying perfusion improves, GFR and urine output typically recover.

Obstruction would cause postrenal AKI, not a pre-renal pattern, and wouldn’t reflect reduced perfusion driving a lower GFR. Oliguria that arises from intrinsic renal damage points to intrarenal injury (like ATN or nephritis), rather than a problem of blood flow to the kidneys.