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Renal Failure Index (RFI)
Distinguishes pre-renal from intrinsic AKI using creatinine ratio
Laboratory Inputs
Required (1–400)
Required (1–800)
Required (0.1–30)
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RFI
| RFI | Interpretation | Mechanism |
|---|---|---|
| < 1 | Pre-renal AKI | Intact tubular function; avid Na and water reabsorption |
| 1–2 | Indeterminate | Overlap; consider clinical context and other indices |
| > 2 | Intrinsic AKI (ATN) | Tubular damage; impaired Na reabsorption |
RFI = UNa / (UCr / SCr)
Equivalent to: RFI = (UNa × SCr) / UCr
Compare: FENa = (UNa × SCr) / (SNa × UCr) × 100
RFI is similar to FENa but does not require serum sodium
Equivalent to: RFI = (UNa × SCr) / UCr
Compare: FENa = (UNa × SCr) / (SNa × UCr) × 100
RFI is similar to FENa but does not require serum sodium
Comparison with FENa: RFI and FENa give similar clinical information. RFI <1 and FENa <1% both indicate pre-renal AKI. RFI has same exceptions as FENa: may be <1 in early contrast nephropathy, pigment nephropathy, and NSAID-induced AKI. Unreliable after diuretic use.
