A 32-year-old man is brought to the emergency department after being trapped under a collapsed wall for 6 hours. He has a swollen, tender right thigh. Urine dipstick shows 3+ blood but urine microscopy shows no red cells. Creatinine has risen to 3.4 mg/dL. Which finding would be most consistent with the underlying cause of his AKI?

• A Fractional excretion of sodium below 1%
• B Serum calcium of 11.2 mg/dL
• C Urine pH of 5.0 with muddy brown casts absent
• D Serum creatine kinase of 48,000 U/L ✓

Explanation

The dipstick-positive, microscopy-negative urine indicates myoglobinuria, and crush injury causes rhabdomyolysis with markedly elevated creatine kinase. Myoglobin precipitates in tubules causing ATN, so FENa is usually above 1% (unlike prerenal azotaemia). Early course features hypocalcaemia due to calcium influx into damaged muscle and phosphate binding, not hypercalcaemia; hypercalcaemia appears later during recovery. Management is aggressive isotonic saline before pigment reaches the tubules.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.