Sodium 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 Sodium:
- Optimal 138 – 142 mEq/L (138 – 142 mmol/L); sufficient 135 – 145 mEq/L (135 – 145 mmol/L); out of range below 135 or above 145 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 | 138 – 142 | 135 – 145 | below 135 or above 145 |
| mmol/L | 138 – 142 | 135 – 145 | below 135 or above 145 |
What the evidence says
The acceptable band is the laboratory reference interval, 135 to 145 mmol/L (MedlinePlus, Mayo Clinic Laboratories); the European guideline defines hyponatraemia as below 135. UK laboratories use a slightly wider harmonised interval of 133 to 146. The optimal band of 138 to 142 comes from a US cohort followed for 25 years, in which that range carried the lowest risk of chronic disease and early death and risk rose above 142. That finding is an association: it has not been shown that changing sodium or fluid intake changes the outcome.
Sources
- Sodium blood test — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2025 · Government / public-health guidanceNormal blood sodium is 135 to 145 mEq/L. Matches Sera's upper edge of 145; the lower edge is 135, not Sera's 136.
- ELPSR - Overview: Electrolyte Panel, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceSerum sodium reference values from age 1: 135 to 145 mmol/L. Same interval as MedlinePlus.
- Clinical practice guideline on diagnosis and treatment of hyponatraemia — Spasovski G, Vanholder R, Allolio B, et al. — Nephrology Dialysis Transplantation (European Renal Best Practice, ESE, ESICM), 2014 · Clinical guidelineDefines hyponatraemia as serum sodium below 135 mmol/L. Published 2014; no later edition of this European guideline was found, so it is cited as the edition in force. Supports a lower edge of 135.
- Sodium (Pathology tests database) — University Hospitals Birmingham NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceUK harmonised interval (Pathology Harmony) 133 to 146 mmol/L, one to two units wider than the US interval at each end.
- Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality — Dmitrieva NI, Gagarin A, Liu D, et al. — eBioMedicine, 2023 · Peer-reviewed publicationUS cohort (ARIC, 11,255 adults, 25 years): sodium of 138 to 142 mmol/L carried the lowest risk of chronic disease and premature death; above 142 the risk of chronic disease was 39% higher. Matches Sera's optimal band of 138 to 142. Observational, not causal.
What Sodium measures
An important electrolyte that controls fluid balance, kept in check by the kidneys.
Sodium is vital for fluid balance, nerve signals, and muscle movement. Abnormal levels can reflect hydration, kidney function, or a hormone imbalance.