A 42-year-old woman presents with fever, maculopapular rash, and acute kidney injury (creatinine 3.8 mg/dL) 10 days after starting pantoprazole for dyspepsia. Urinalysis shows sterile pyuria and mild proteinuria. Eosinophil count is 1200/microL. Which finding would most strongly support the diagnosis?
- A FENa <1% with granular casts
- B Red cell casts on urine microscopy
- C Urine eosinophils on Hansel stain ✓
- D Positive anti-dsDNA antibodies
Correct answer: C. Urine eosinophils on Hansel stain
Explanation
Acute interstitial nephritis (AIN) is a drug-induced hypersensitivity reaction. The triad of fever, rash, and eosinophilia with recent drug exposure is classic. Urine eosinophils (Hansel stain) support the diagnosis, though sensitivity is modest. Red cell casts suggest glomerulonephritis. FENa <1% suggests pre-renal AKI. Anti-dsDNA suggests lupus nephritis. Sterile pyuria is characteristic of AIN.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.