Renal Failure Index Calculation formula

The renal failure index is an indicator that helps in distinguishing prerenal azotemia from oliguric acute renal failure. It can be calculated from measurements of urinary sodium, urinary creatinine and serum creatinine.

Renal Failure Index = (Urine Sodium × Serum Creatinine) ÷ Urine Creatinine

For example,

If,

Urine Na = 20 mEq/L

Urine Creatinine = 1.40 mg/dL

Serum Creatinine = 1.50 mg/dL

Then,

Renal Failure Index = 21.43

Note: An RFI <1 is consistent with prerenal failure while an RFI >1 goes with ATN (acute tubular necrosis).

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