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what is fractional excretion of sodium?

what are the differences between pre renal and renal failure?


Fractional excretion of sodium is excreted load of sodium divided by filtered load of sodium or to put it in other way
FeNa+ = (V X UNa+) / (GFR X PNa+) where V is urine flow rate and PNa+ and UNa+ are plasma and urine Na+ conc.

In pre-renal failure due to decreased renal perfusion the kidneys try to conserve as much sodium so as to increase plasma volume and hence renal perfusion. So FENa+ will be less in pre-renal failure compared to intrinsic renal failure. I don't remember the values though.


thanks good explanation..FENa+ less than 1%is typical of pre-renal failure..
in renal (ATN)FENa+ is greater than 2% due to failure to reabsorb

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