Postrenal AKI vs Intrinsic AKI
How to tell Postrenal AKI and Intrinsic AKI apart when a board question makes them look alike.
Postrenal AKI: outflow obstruction with hydronephrosis on ultrasound; intrinsic AKI: parenchymal injury with active urine sediment.
Side by side
AKI from urinary outflow obstruction, suggested by retention, suprapubic fullness, hydronephrosis, BPH, stones, pelvic tumor, or catheter blockage.
AKI from direct kidney parenchymal injury such as ATN, glomerulonephritis, interstitial nephritis, vascular disease, or toxins.
Obstruction raises upstream pressure, lowers net filtration pressure, and can injure tubules if not relieved.
The kidney tissue itself is damaged, producing characteristic sediment or impaired tubular handling depending on the cause.
Hydronephrosis on ultrasound, distended bladder, anuria/retention, or relief after catheterization points postrenal AKI.
Muddy brown casts, RBC casts, WBC casts, eosinophiluria, heavy proteinuria, or FeNa above 2% in ATN points intrinsic AKI.
The trap
Late obstruction can mimic intrinsic tubular injury, so image for hydronephrosis when obstruction is plausible.
Watch it explained
The repair move
For AKI, decide whether flow to kidney, kidney tissue, or urine outflow is the failing compartment.
Try a free question
CoreAn older man with BPH develops acute kidney injury, suprapubic fullness, bilateral hydronephrosis, and urinary retention. Which AKI category is most likely?
Show answer and explanation
Answer: A. Postrenal AKI. Postrenal AKI is caused by urinary outflow obstruction and is suggested by retention, hydronephrosis, BPH, stones, tumors, or catheter obstruction.
Why the other choices are tempting
- B. Intrinsic AKI is direct kidney parenchymal injury.
- C. Prerenal AKI is renal hypoperfusion with intact tubules early.
- D. AIN is a drug/allergy-pattern intrinsic kidney injury.
- E. Minimal change disease causes nephrotic syndrome.
Flashcards
Tap a card to flip it.
What is the fastest separator for Postrenal AKI vs Intrinsic AKI?
Postrenal AKI: outflow obstruction with hydronephrosis on ultrasound; intrinsic AKI: parenchymal injury with active urine sediment.
What clue should make you choose Postrenal AKI?
AKI from urinary outflow obstruction, suggested by retention, suprapubic fullness, hydronephrosis, BPH, stones, pelvic tumor, or catheter blockage.
Quick answers
What is the fastest way to tell Postrenal AKI from Intrinsic AKI?
Postrenal AKI: outflow obstruction with hydronephrosis on ultrasound; intrinsic AKI: parenchymal injury with active urine sediment.
What is the key clue for Postrenal AKI?
AKI from urinary outflow obstruction, suggested by retention, suprapubic fullness, hydronephrosis, BPH, stones, pelvic tumor, or catheter blockage.
What is the key clue for Intrinsic AKI?
AKI from direct kidney parenchymal injury such as ATN, glomerulonephritis, interstitial nephritis, vascular disease, or toxins.
What is the common trap with Postrenal AKI vs Intrinsic AKI?
Late obstruction can mimic intrinsic tubular injury, so image for hydronephrosis when obstruction is plausible.