Which of the following findings supports acute interstitial nephritis in a patient with rising creatinine and eosinophiluria?

• A. Eosinophils in urine.
• B. Hyperkalemia.
• C. Hypokalemia.
• D. Hyperbilirubinemia.

Answer: (A)

Eosinophiluria is a key clue for acute interstitial nephritis, which is often driven by a drug-induced hypersensitivity reaction and presents with a rising creatinine. The presence of eosinophils in the urine supports the diagnosis because the inflammatory process in the interstitium frequently releases eosinophils into the urine. Other findings listed are less specific: hyperkalemia can occur with many causes of acute kidney injury and is not unique to AIN; hypokalemia is not typical in this setting; hyperbilirubinemia points toward liver or biliary disease rather than interstitial nephritis. So the urinary eosinophils provide the strongest supportive evidence here.