FENa (Fractional Excretion of Sodium)

Espinel CH. The FENa test: use in the differential diagnosis of acute renal failure. In oliguric acute renal failure a fractional sodium excretion below 1% pointed to a prerenal cause and above 1% (usually well above) to acute tubular necrosis.

Steiner RW. Interpreting the fractional excretion of sodium. Reviews the test’s diagnostic limits — it is unreliable after loop diuretics, in chronic kidney disease, contrast nephropathy, rhabdomyolysis, and acute glomerulonephritis, where FEUrea may be preferred.