A 65-year-old woman develops AKI after contrast-enhanced CT. Creatinine rises from 1.1 to 1.8 mg/dL at 48 hours. Urine sodium is 14 mEq/L, urine osmolality 520 mOsm/kg. FENa is 0.6%. What does this suggest about the etiology?
- A Pre-renal AKI due to volume depletion ✓
- B Acute tubular necrosis (intrinsic AKI)
- C Contrast-induced nephropathy with tubular injury pattern
- D Obstructive uropathy
Correct answer: A. Pre-renal AKI due to volume depletion
Explanation
A FENa of 0.6% (<1%) with concentrated urine (osmolality >500 mOsm/kg) indicates intact tubular reabsorption and suggests pre-renal AKI (or early hepatorenal syndrome). Acute tubular necrosis typically shows FENa >2% with dilute urine (osmolality <350 mOsm/kg) and muddy brown casts. Contrast-induced nephropathy can initially show features of pre-renal AKI if volume depletion is the predominant mechanism; true tubular injury shows higher FENa. Obstructive AKI presents with variable FENa depending on chronicity.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.