Which constellation most strongly supports acute interstitial nephritis?

Which constellation most strongly supports acute interstitial nephritis?

• A. AKI with eosinophils, fever, maculopapular rash and WBC casts
• B. Nephrotic-range proteinuria with hyaline casts
• C. Acute tubular necrosis with muddy brown casts
• D. Chronic kidney disease with small kidneys

Answer: (A)

Acute interstitial nephritis is an inflammatory injury of the renal interstitium, usually drug-induced, that classically presents as an acute kidney injury with signs of a hypersensitivity reaction. The most telling clue is the combination of fever and a maculopapular rash along with urinalysis findings of eosinophils and white blood cell casts. Eosinophiluria—often detected with a special stain—reflects eosinophilic infiltration of the interstitium and supports the diagnosis of AIN. This pattern is different from other kidney injuries: nephrotic-range proteinuria with hyaline casts points toward glomerular or tubular proteinuria rather than interstitial inflammation; muddy brown casts are typical of acute tubular necrosis from ischemia or toxins; and chronically small kidneys suggest long-standing chronic kidney disease rather than an acute hypersensitivity process.

Acute interstitial nephritis is an inflammatory injury of the renal interstitium, usually drug-induced, that classically presents as an acute kidney injury with signs of a hypersensitivity reaction. The most telling clue is the combination of fever and a maculopapular rash along with urinalysis findings of eosinophils and white blood cell casts. Eosinophiluria—often detected with a special stain—reflects eosinophilic infiltration of the interstitium and supports the diagnosis of AIN. This pattern is different from other kidney injuries: nephrotic-range proteinuria with hyaline casts points toward glomerular or tubular proteinuria rather than interstitial inflammation; muddy brown casts are typical of acute tubular necrosis from ischemia or toxins; and chronically small kidneys suggest long-standing chronic kidney disease rather than an acute hypersensitivity process.