A 28-year-old man is rescued after being trapped under rubble for 14 hours. He develops oliguria with creatinine rising from 1.0 to 5.8 mg/dL. Urine dipstick tests strongly positive for blood, but urine microscopy shows no red cells. The most likely cause of his AKI is:

• A IgA nephropathy
• B Acute interstitial nephritis
• C Myoglobin cast nephropathy ✓
• D Cortical necrosis

Explanation

The dipstick heme test detects peroxidase activity of hemoglobin and myoglobin alike. Crush injury releases myoglobin, which precipitates with Tamm-Horsfall protein in acidic tubular fluid causing pigment cast nephropathy, giving dipstick-positive urine with no intact erythrocytes on microscopy. Interstitial nephritis shows WBCs and casts, IgA nephropathy shows dysmorphic red cells and red cell casts, and cortical necrosis gives gross haematuria with visible red cells.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.