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Zorluk: OrtaNephrology

A 68-year-old man is evaluated in the hospital for decreased urine output. He was admitted 3 days ago for severe community-acquired pneumonia and has been receiving intravenous antibiotics. His blood pressure is 98/60 mm Hg and heart rate is 102/min. Physical examination shows dry mucous membranes and flat jugular veins. Laboratory studies are obtained to evaluate his acute kidney injury:

Laboratory TestResult
Serum sodium135 mEq/L
Serum creatinine1.5 mg/dL
Blood urea nitrogen38 mg/dL
Urine sodium27 mEq/L
Urine creatinine60 mg/dL

What is the patient's fractional excretion of sodium (FeNa) expressed as a percentage?

Cevap: 0.5 %

Cevap

0.5
The correct calculation yields a fractional excretion of sodium (FeNa) of exactly 0.5%. A FeNa of < 1% indicates a prerenal etiology for acute kidney injury. In this patient, signs of volume depletion (hypotension, tachycardia, dry mucous membranes) point toward prerenal azotemia secondary to dehydration, leading the kidneys to avidly reabsorb sodium and water in an attempt to restore intravascular volume.

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1
Identify the formula for Fractional Excretion of Sodium (FeNa).
FeNa=UNa×PCrPNa×UCr×100FeNa = \frac{U_{Na} \times P_{Cr}}{P_{Na} \times U_{Cr}} \times 100
This formula relates the amount of sodium excreted to the amount of creatinine excreted, thereby correcting for urine concentration.
2
Extract the necessary values from the provided laboratory table.
UNa=27U_{Na} = 27 mEq/L, PCr=1.5P_{Cr} = 1.5 mg/dL, PNa=135P_{Na} = 135 mEq/L, and UCr=60U_{Cr} = 60 mg/dL.
These specific variables are required for the FeNa equation. The Blood Urea Nitrogen (BUN) value of 38 mg/dL is a distractor for this specific calculation.
3
Substitute the values into the FeNa equation.
FeNa=27×1.5135×60×100FeNa = \frac{27 \times 1.5}{135 \times 60} \times 100
Plugging the values into the correct positions in the numerator and denominator ensures mathematical accuracy.
4
Perform the arithmetic calculation.
40.58100×100=0.005×100=0.5\frac{40.5}{8100} \times 100 = 0.005 \times 100 = 0.5
This yields the final FeNa value as a percentage, which can then be interpreted clinically.

Anahtar Kavram

Calculation and interpretation of Fractional Excretion of Sodium (FeNa) in the evaluation of Acute Kidney Injury.
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Nephrology

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