RENAL PHYSIOLOGY-FRACTIONAL EXCRETION OF SODIUM
SUMMARY
1. The fractional excretion of sodium (FENa) is the ratio of excreted Na+ to the total filtered load of Na+.
2. It is used to differentiate prerenal azotemia (FENa < I%, high levels of nitrogen-containing compounds such as creatinine and urea) from acute tubular necrosis (FENa > 2%, ATN).
3. Other causes of AKI with FENa < I% include: contrast induced ATN, cardio-renal syndrome, hepato-renal syndrome, non-oliguric ATN, pigment nephropathy & acute glomerulonephritis.
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