FENa / FEUrea

Fractional excretion of sodium: (urine Na × serum Cr) ÷ (serum Na × urine Cr) × 100. FEUrea substitutes urea for sodium when diuretics are on board.

Urine sodium(mmol/L)Serum creatinine(µmol/L)Serum sodium(mmol/L)Urine creatinine(µmol/L)

Result

Fill the inputs to compute.

Interpretation: Reads whether the tubules are avidly holding sodium (prerenal) or wasting it (ATN).
Limitations: Invalidated by diuretics; can be low in contrast nephropathy, early GN, and pigment nephropathy despite intrinsic injury.
Reference: Espinel CH. JAMA 1976;236:579-81; Carvounis CP et al. Kidney Int 2002;62:2223-9.

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