Potassium optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for Potassium:
- Optimal 4 – 4.5 mEq/L (4 – 4.5 mmol/L); sufficient 3.5 – 5 mEq/L (3.5 – 5 mmol/L); out of range below 3.5 or above 5 mEq/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mEq/L | 4 – 4.5 | 3.5 – 5 | below 3.5 or above 5 |
| mmol/L | 4 – 4.5 | 3.5 – 5 | below 3.5 or above 5 |
What the evidence says
Haemolysis during collection raises potassium artefactually. An unexpected high value is worth repeating before it is interpreted. The acceptable band of 3.5 to 5.0 mmol/L is the conventional interval; in a pooled analysis of 1.2 million people, mortality was higher outside it. Laboratory upper limits run slightly higher, 5.2 in the US sources and 5.3 in the UK, so a result of 5.1 to 5.3 may be printed as normal on the report. The optimal band of 4.0 to 4.5 is where the same analysis found the lowest risk; that is an association, not a treatment target.
Sources
- Serum potassium and adverse outcomes across the range of kidney function: a CKD Prognosis Consortium meta-analysis — Kovesdy CP, Matsushita K, Sang Y, et al. — European Heart Journal, 2018 · Peer-reviewed publicationPooled 27 international cohorts (1,217,986 people): mortality was lowest at potassium 4 to 4.5 mmol/L and higher outside 3.5 to 5 mmol/L. Supports Sera's acceptable band of 3.5 to 5.0 and an optimal band of 4.0 to 4.5. The cohorts include some outside Europe and North America.
- Potassium (Pathology tests database) — University Hospitals Birmingham NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceUK harmonised adult interval (Pathology Harmony) 3.5 to 5.3 mmol/L. Matches Sera's lower edge of 3.5; the upper limit is 0.3 higher than Sera's.
- ELPSR - Overview: Electrolyte Panel, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceSerum potassium reference values from age 1: 3.6 to 5.2 mmol/L. Upper limit 0.2 above Sera's 5.0.
- Potassium test — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2025 · Government / public-health guidanceNormal range 3.7 to 5.2 mEq/L. Upper limit 0.2 above Sera's 5.0.
What Potassium measures
An important electrolyte for the heart and muscles, balanced by the kidneys.
Potassium is vital for a steady heart rhythm, muscle function, and nerve signals. Both high and low levels are a concern and can be affected by kidney function and by some medicines.