A 54-year-old man is evaluated in the hospital for decreased urine output. He was admitted 7 days ago for infective endocarditis and has been receiving intravenous vancomycin and gentamicin. Over the past 24 hours, his urine output has dropped to 300 mL. His vital signs are within normal limits and he appears euvolemic on examination. Laboratory studies show the following:
| Laboratory Parameter | Serum | Urine |
|---|---|---|
| Sodium | 140 mEq/L | 70 mEq/L |
| Potassium | 5.2 mEq/L | 25 mEq/L |
| Creatinine | 4.0 mg/dL | 50 mg/dL |
| Urea nitrogen (BUN) | 40 mg/dL | - |
| Osmolality | 290 mOsm/kg H₂O | 310 mOsm/kg H₂O |
Microscopic urinalysis reveals muddy brown granular casts.
Based on the provided laboratory findings, what is this patient's fractional excretion of sodium ()? (Express your answer as a percentage)
Cevap: 4 %
Cevap
4.0
The fractional excretion of sodium () measures the percentage of filtered sodium that is ultimately excreted in the urine. It is calculated using the formula: . Plugging in the correctly extracted values from the table (, , , ) yields . A value greater than 2% in the setting of oliguria is highly suggestive of intrinsic acute kidney injury, specifically acute tubular necrosis (ATN). This correlates perfectly with the patient's history of aminoglycoside (gentamicin) use, isotonic urine (osmolality ~300 mOsm/kg), and the pathognomonic finding of muddy brown granular casts on urinalysis.
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The Fractional Excretion of Sodium (FeNa) is calculated to differentiate prerenal azotemia (FeNa < 1%) from intrinsic acute kidney injury (FeNa > 2%).