A 57-year-old woman is admitted to the intensive care unit (ICU) after being involved in a highway motor vehicle accident. She was hypotensive at the scene and received 7 L of fluids, which included crystalloids, blood, and fresh frozen plasma. She had significant external blood loss from multiple fractures and skin loss. She undergoes surgery, after which she is transferred to the ICU and receives continuous IV fluids and vasopressors. Her laboratory studies 24 hours after the accident show the following: Which of the following is the most likely microscopic finding on urinalysis?

Question

A 57-year-old woman is admitted to the intensive care unit (ICU) after being involved in a highway motor vehicle accident.  She was hypotensive at the scene and received 7 L of fluids, which included crystalloids, blood, and fresh frozen plasma.  She had significant external blood loss from multiple fractures and skin loss.  She undergoes surgery, after which she is transferred to the ICU and receives continuous IV fluids and vasopressors.  Her laboratory studies 24 hours after the accident show the following:  Which of the following is the most likely microscopic finding on urinalysis?

Quizplus · Accepted Answer

The clinical picture of this patient is highly suggestive of acute tubular necrosis (ATN) following hypovolemic shock. A serum BUN-to-creatinine ratio of 10-15 is typically seen in ATN (in contrast to prerenal azotemia, where the ratio is >20). Other findings that support this diagnosis are: Urine osmolality of 300-350 mOsm/L (but never <300) Urine Na of >20 mEq/L FENa >2% Urine osmolality of 300-350 mOsm/L (but never <300) Urine Na of >20 mEq/L FENa >2% Prolonged hypotension from any cause can lead to ATN. The hallmark findings on urinalysis are muddy brown granular casts consisting of renal tubular epithelial cells; this is a nonspecific but very sensitive finding for ATN. (Choice A) Broad casts are seen in patients with chronic kidney disease (CKD). These arise in the dilated tubules of enlarged nephrons that have undergone compensatory hypertrophy in response to the reduced renal mass. Waxy casts, which are shiny and translucent, are also generally seen in CKD. (Choice C) Red blood cell casts are indicative of glomerular disease or vasculitis. (Choice D) White blood cell (WBC) casts are definitive evidence that urinary WBCs originate in the kidney. These are seen in cases of interstitial nephritis, pyelonephritis, etc. (Choice E) Fatty casts are seen in conditions causing nephrotic syndrome. Hyaline casts are composed almost entirely of protein and pass unchanged along the urinary tract; these may be seen in asymptomatic individuals and in patients with pre-renal azotemia. (Choice F) Urine eosinophilia is classically associated with interstitial nephritis. Educational objective: Muddy brown granular cast - Acute tubular necrosis Red blood cell casts - Glomerulonephritis White blood cell casts - Interstitial nephritis and pyelonephritis Fatty casts - Nephrotic syndrome Broad and waxy casts - Chronic renal failure *Extremely high yield question for the USMLE!!!

A 57-Year-Old Woman Is Admitted to the Intensive Care Unit