A 68-year-old woman is evaluated in the hospital for decreased urine output. She was admitted 2 days ago for severe gastroenteritis. Her past medical history is significant for hypertension treated with amlodipine. Her blood pressure is 98/60 mm Hg, and her pulse is 112/min. Mucous membranes are dry. Laboratory studies show the following:
| Test | Result |
|---|---|
| Serum sodium | 140 mEq/L |
| Serum potassium | 3.8 mEq/L |
| Serum chloride | 102 mEq/L |
| Blood urea nitrogen | 42 mg/dL |
| Serum creatinine | 2.0 mg/dL |
| Urine sodium | 14 mEq/L |
| Urine creatinine | 40 mg/dL |
Based on the laboratory results provided, what is the patient's fractional excretion of sodium (FENa)? Give your answer as a percentage.
Answer: 0.5 %
Answer
0.5
The fractional excretion of sodium (FENa) evaluates the percentage of sodium filtered by the glomeruli that is eventually excreted in the urine. It is calculated using the formula: . Plugging the patient's laboratory values into this formula yields . A FENa of less than 1% indicates a prerenal etiology for the patient's acute kidney injury, which is consistent with her history of severe gastroenteritis and clinical signs of profound volume depletion.
Step-by-Step Solution
Key Concept
Calculating the fractional excretion of sodium (FENa) to determine the etiology of acute kidney injury.
Estimated Time:1m 0s