Fena may refer to:

• FENA, the Federal News Agency of the republic of Bosnia and Herzegovina
• Fractional sodium excretion (FE_Na), a medical parameter representing the fraction of sodium in urine relative to the fraction of sodium in circulation
• Fena Lake, the largest lake on the island of Guam

The fractional excretion of sodium (FE_Na) is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is measured in terms of plasma and urine sodium, rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption. Therefore the urinary and plasma concentrations of sodium must be compared to get an accurate picture of renal clearance. In clinical use, the fractional excretion of sodium can be calculated as part of the evaluation of acute kidney failure in order to determine if hypovolemia or decreased effective circulating plasma volume is a contributor to the kidney failure.