What this calculator does
Fractional excretion of sodium (FeNa) works out compares urine and plasma sodium and creatinine to help classify acute kidney injury. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
The inputs explained
| Field | What to enter |
|---|---|
| Plasma sodium (mEq/L) | A number, measured in mEq/L. Starts at 140. |
| Urine sodium (mEq/L) | A number, measured in mEq/L. Starts at 20. |
| Plasma creatinine (mg/dL) | A number, measured in mg/dL. Starts at 1. |
| Urine creatinine (mg/dL) | A number, measured in mg/dL. Starts at 60. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with plasma sodium
Every other input is held at the calculator’s starting values while plasma sodium varies. Select any row to load that scenario into the calculator.
| Plasma sodium (mEq/L) | FeNa | Reading | Note |
|---|---|---|---|
| 70 | 0.476% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |
| 105 | 0.317% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |
| 140 | 0.238% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |
| 210 | 0.159% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |
| 280 | 0.119% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |
| 420 | 0.079% | Under 1%: suggests a prerenal cause (reduced blood flow to the kidneys) | Validated for acute kidney injury only, and unreliable in patients taking diuretics. |