If a suspected drug-induced interstitial nephritis does not improve after removing the offending agent, which test is the gold standard for dx?

If a suspected drug-induced interstitial nephritis does not improve after removing the offending agent, which test is the gold standard for dx?

• A. Renal ultrasound.
• B. Renal biopsy.
• C. Urine culture.
• D. Serum creatinine repeat.

Answer: (B)

The key idea is that confirming drug-induced interstitial nephritis requires tissue evidence. If removing the offending drug doesn’t yield improvement, a renal biopsy provides histologic confirmation of interstitial inflammation and edema (often with eosinophils and tubulitis), which distinguishes this condition from other causes of kidney injury such as acute tubular necrosis or glomerulonephritis and guides management. Imaging like renal ultrasound can help rule out obstruction but doesn’t diagnose DIIN, urine culture checks for infection, and repeating the serum creatinine only tracks function without establishing the cause.

The key idea is that confirming drug-induced interstitial nephritis requires tissue evidence. If removing the offending drug doesn’t yield improvement, a renal biopsy provides histologic confirmation of interstitial inflammation and edema (often with eosinophils and tubulitis), which distinguishes this condition from other causes of kidney injury such as acute tubular necrosis or glomerulonephritis and guides management. Imaging like renal ultrasound can help rule out obstruction but doesn’t diagnose DIIN, urine culture checks for infection, and repeating the serum creatinine only tracks function without establishing the cause.