Acute interstitial nephritis

1. Big picture

Acute interstitial nephritis (AIN), also called acute tubulointerstitial nephritis, is an important cause of intrinsic acute kidney injury (AKI). It is most often a drug-induced hypersensitivity reaction affecting the renal interstitium and tubules.

The exam pattern is:

Recent new drug → rising creatinine → fever/rash/arthralgia may occur → sterile pyuria, leukocyte casts, eosinophilia/eosinophiluria → stop the drug.

The classic triad of fever + rash + eosinophilia is high-yield, but it is not always present. Do not wait for the full triad.