AIN vs ATN
How to tell AIN and ATN apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
White blood cell casts after a recent culprit drug favor AIN, while muddy brown granular casts favor ATN.
Side by side
Acute kidney injury after new medication with sterile pyuria, white blood cell casts, and possible rash or fever suggests acute interstitial nephritis.
Acute kidney injury after ischemia or nephrotoxin exposure with muddy brown granular casts suggests acute tubular necrosis.
AIN is an immune-mediated interstitial inflammation, commonly drug-induced, that impairs tubular function.
ATN results from tubular epithelial injury and necrosis from hypoperfusion or direct nephrotoxicity.
Urinalysis often shows pyuria, white blood cell casts, mild proteinuria, and eosinophiluria in some cases; fractional excretion of sodium can be variable and is not diagnostic.
Urinalysis shows muddy brown granular casts and tubular epithelial cells; FeNa is often above 2% in established ATN and BUN:Cr ratio is often around 10 to 15:1.
The trap
Eosinophils are overvalued and may be absent in true AIN, while ATN may be mislabeled as AIN after ICU antibiotic exposure. Urine sediment pattern and exposure timeline are more reliable than eosinophil testing alone.
The repair move
Next best step: stop the suspected offending drug immediately and provide supportive renal care, then monitor creatinine and urine output daily. If kidney function fails to improve within 3 to 5 days or biopsy confirms severe interstitial inflammation, start prednisone about 1 mg/kg/day with taper over 2 to 6 weeks.
Try a free question
CoreA 69-year-old woman develops acute kidney injury after septic shock recovery. BP 118/72 mm Hg, HR 92/min, temp 37.2 C. Urine microscopy shows abundant muddy brown granular casts. What is the most likely diagnosis?
Show answer and explanation
Answer: B. Acute tubular necrosis. Muddy brown granular casts in the setting of ischemic insult are most consistent with ATN.
Why the other choices are tempting
- A. AIN is less likely because white blood cell casts and drug hypersensitivity pattern are not present.
- C. Prerenal azotemia generally has bland sediment without granular casts.
- D. Postrenal obstruction requires obstructive findings such as hydronephrosis.
- E. RPGN would usually present with red blood cell casts and nephritic features.
Flashcards
Tap a card to flip it.
Which urine sediment finding most strongly supports AIN over ATN?
White blood cell casts support AIN over ATN.
Which sediment clue is most characteristic of ATN?
Muddy brown granular casts are classic for ATN.
Quick answers
What is the fastest way to tell AIN from ATN?
White blood cell casts after a recent culprit drug favor AIN, while muddy brown granular casts favor ATN.
What is the key clue for AIN?
Acute kidney injury after new medication with sterile pyuria, white blood cell casts, and possible rash or fever suggests acute interstitial nephritis.
What is the key clue for ATN?
Acute kidney injury after ischemia or nephrotoxin exposure with muddy brown granular casts suggests acute tubular necrosis.
What is the common trap with AIN vs ATN?
Eosinophils are overvalued and may be absent in true AIN, while ATN may be mislabeled as AIN after ICU antibiotic exposure. Urine sediment pattern and exposure timeline are more reliable than eosinophil testing alone.