Equations
RFI = Urine_Na * Plasma_Cr / Urine_Cr
Fractional excretion of sodium (FE-Na) =
100 * ((Urine_Na in mEq/L) / (plasma_Na in mEq/L)) /
((Urine Cr in mg/dL) / (plasma Cr in mg/dL))
(FE-Na < 1%) seen in: pre-renal azotemia and acute
glomerulonephritis. Also seen in 5-10% of nonoliguric or x-ray contrast induced
ATN, and early sepsis.
(FE-Na > 1% ) Seen in most cases of ATN. Also seen in pre-existing chronic renal failure, and after diuretic administration.
[References:]
Durakovic Z, Durakovic A, Durakovic S. The lack of clinical value of laboratory parameters in predicting outcome in acute renal failure.
Ren Fail 1989-90;11(4):213-9.
Porush JG. New concepts in acute renal failure. Am Fam Physician 1986 Mar;33(3):109-18.
Myers BD, Hilberman M, Spencer RJ, Jamison RL. Glomerular and tubular function in
non-oliguric acute renal failure. Am J Med 1982 Apr; 72(4): 642-9.
Miller TR, Anderson RJ, Linas SL, Henrich WL, Berns AS, Gabow PA, Schrier RW.
Urinary diagnostic indices in acute renal failure: a prospective study. Ann Intern Med 1978 Jul;89(1):47-50.
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