Acute Tubular Necrosis

A 38-year-old woman with a history of severe dehydration and hypotension following acute gastroenteritis develops acute kidney injury. Urine osmolality is 450 mOsm/kg, urine sodium is 15 mEq/L, and serum creatinine is 3.2 mg/dL. To differentiate between prerenal azotemia and acute tubular necrosis, which investigation would be most appropriate?

A 42-year-old woman is admitted with acute kidney injury following rhabdomyolysis from a crush injury. Serum myoglobin is elevated, and urinalysis shows dark brown urine with positive dipstick for blood but no RBCs on microscopy. Which investigation is most appropriate to confirm myoglobin-induced acute tubular necrosis and assess severity?

A 58-year-old man with diabetes mellitus presents with acute kidney injury following sepsis from a urinary tract infection. Serum creatinine has risen from 1.2 to 4.8 mg/dL over 48 hours. Urine output is 200 mL/24 hours. Urinalysis shows muddy brown casts and fractional excretion of sodium (FENa) is 3.2%. Which investigation is most specific for confirming the diagnosis of acute tubular necrosis?

A 42-year-old woman with severe sepsis secondary to urosepsis is admitted to the ICU. She develops acute kidney injury with serum creatinine 3.8 mg/dL, oliguria (urine output 150 mL/24 h), and muddy brown casts on urinalysis. FENa is 3.2%. She is hypotensive (BP 88/52 mmHg) despite 2 L of crystalloid resuscitation. Blood cultures are pending. What is the first-line pharmacological agent to improve renal perfusion in sepsis-induced acute tubular necrosis?

A 58-year-old man with diabetes mellitus presents with acute kidney injury following a contrast-enhanced CT angiography for suspected pulmonary embolism. His urine microscopy shows muddy brown casts and granular casts. Which histopathological feature best distinguishes acute tubular necrosis (ATN) from acute interstitial nephritis (AIN)?