Electrolyte-Free Water Clearance
Electrolyte-free water clearance (Rose 1986): urine volume × [1 − (urine Na + urine K) / plasma Na]; a positive value means the kidney is excreting free water, a negative value means net free-water retention.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Urine sodium
- 20 mEq/L
- Urine potassium
- 10 mEq/L
- Plasma sodium
- 140 mEq/L
- Urine volume over the interval
- 2000 mL
Result: EFWC +1571.4 — the kidney is excreting free water (aggravating hypernatremia / correcting hyponatremia).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Sign
- Positive = kidney excreting free water (aggravating hypernatremia / correcting hyponatremia); negative = net free-water retention (aggravating hyponatremia). Decision support, not a fluid order.
What you enter
- Urine sodium
- Urine potassium
- Plasma sodium
- Urine volume over the interval
How this is calculated
- Formula
- EFWC = V × [1 − (U_Na + U_K) / P_Na], reported per collection interval in the same volume unit as V.
Rose BD. New approach to disturbances in the plasma sodium concentration. Am J Med. 1986;81(6):1033-1040. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.