Which finding is characteristic of acute interstitial nephritis?

• A. Eosinophils in the urine
• B. Hematuria
• C. Proteinuria
• D. Bacteria in urine

Answer: (A)

Acute interstitial nephritis is a drug-triggered hypersensitivity reaction affecting the kidney interstitium. A key urinary clue is eosinophils in the urine, often seen on special stains (Hansel stain). This reflects the eosinophilic inflammatory infiltrate in the interstitium and supports the diagnosis in the right clinical context (recent new medication, fever or rash, elevated creatinine).

While hematuria or proteinuria can occur in various renal conditions and are not specific, the presence of eosinophils in the urine is particularly characteristic for this condition. Bacteria in the urine would point toward a bacterial infection rather than AIN, which is typically sterile pyuria.