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Urinary indices
Renal Failure Index (RFI) and
Fractional excretion of sodium (FE-Na) 

Calculator

Urine Sodium (UNa): meq/L
Plasma Sodium (PNa): meq/L
Plasma creatinine (PCr): mg/dl
Urine Creatinine (UCr): mg/dl

Background / References:

Analysis


Suggestive of prerenal azotemia or glomerulonephritis
Urinary Na+ <20 mEq/L
Urine/plasma Cr ratio >30
Renal failure index (RFI) <1
urine/plasma osmolality ratio: >1.4
Fe-Na < 1%

Suggestive of ATN or postrenal azotemia:
Urinary Na+ >40 mEq/L
Urine/plasma Creat ratio <20
Renal failure index (RFI) >1
urine/plasma osmolality ratio: 1.0
Fe-Na > 2-3%

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.

Disclaimer

All calculations must be confirmed before use. The authors make no claims of the accuracy of the information contained herein; and these suggested doses are not a substitute for clinical judgement. Neither GlobalRPh Inc. nor any other party involved in the preparation of this program shall be liable for any special, consequential, or exemplary damages resulting in whole or part from any user's use of or reliance upon this material.PLEASE READ THE DISCLAIMER CAREFULLY BEFORE ACCESSING OR USING THIS SITE. BY ACCESSING OR USING THIS SITE, YOU AGREE TO BE BOUND BY THE TERMS AND CONDITIONS SET FORTH IN THE DISCLAIMER.   Read the disclaimer
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