The fractional excretion of sodium is defined as the percentage of the sodium filtered by the kidney. FeNa is defined in terms of plasma and urine sodium. The urinary sodium concentrations of sodium is being referenced with plasma sodim concentration to get an accurate picture of renal clearance. FeNa Calculation is for the evaluation of acute kidney failure.
FeNa is calculated by finding how much sodium is excreted in the urine, and then by the ratio of the total amount of sodium that is filtered by the kidney.
The result is a percentage: if it is lower than 1% it is prerenal disease and if it is higher than 2% it is intrinsic disease; such as acute tubular necrosis.
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