Fractional excretion of sodium
percentage of kidney-filtered sodium excreted in urine
The fractional excretion of sodium (FENa) 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 kidney 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.
Calculation
FENa is calculated in two parts—figuring out how much sodium is excreted in the urine, and then finding its ratio to the total amount of sodium that passed through (a.k.a. "filtered by") the kidney.
First, the actual amount of sodium excreted is calculated by multiplying the urine sodium concentration by the urinary flow rate (UFR). This is the numerator in the equation. The denominator is the total amount of sodium filtered by the kidneys. This is calculated by multiplying the plasma sodium concentration by the glomerular filtration rate (GFR) calculated using creatinine filtration.
“Fractional excretion of sodium” enters the record as percentage of kidney-filtered sodium excreted in urine. Crown Archives preserves that source wording while asking what Fractional, excretion and sodium can confirm, complicate or overturn.
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This entry incorporates text from “Fractional excretion of sodium” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.