In intrinsic AKI due to acute tubular necrosis, which combination of urine sediment findings and FeNa is typical?

• A. Muddy brown granular casts; FeNa often >2%.
• B. Eosinophilic casts; FeNa <1%.
• C. White blood cell casts; FeNa >3%.
• D. Fatty casts; FeNa 1-2%.],

Answer: (D)

In intrinsic AKI from acute tubular necrosis, the tubules are damaged and shed tubular cells into the urine. This produces muddy brown granular casts, which are classic for ATN. Because the tubular injury impairs sodium reabsorption, the kidney leaks more sodium into urine, so the fractional excretion of sodium (FeNa) tends to be elevated, typically above 2%.

So the combination you’d expect is muddy brown granular casts with FeNa > 2%. Other sediment findings point to different processes: eosinophilic casts suggest allergic interstitial nephritis; white blood cell casts can be seen with tubulointerstitial inflammation; fatty casts reflect nephrotic-range proteinuria rather than ATN.