Fractional excretion of potassium (FEK)
Percent of filtered potassium excreted in urine.
Inputs
0 of 4mEq/L
mEq/L
Plasma creatinine
Patient values are shared with every calculator.
When to use
- Hypokalemia workup: renal versus extrarenal loss.
Pearls and pitfalls
- In hypokalemia, FEK above about 6.5% suggests renal loss.
- Rises as GFR falls; interpret with kidney function.
Why use
A simple renal-loss check alongside TTKG.
FEK (%) = (urine K × plasma Cr) ÷ (plasma K × urine Cr) × 100