Bicarbonate (CO2) 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 Bicarbonate (CO2):
- Optimal 22 – 29 mmol/L (22 – 29 mEq/L); out of range below 22 or above 29 mmol/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 |
|---|---|---|---|
| mmol/L | 22 – 29 | — | below 22 or above 29 |
| mEq/L | 22 – 29 | — | below 22 or above 29 |
No separate Sufficient band is currently defined for this marker.
What the evidence says
Reported as bicarbonate or total CO2; the two are used interchangeably on a metabolic panel. The band is the adult laboratory reference interval, 22 to 29 mmol/L, used by Mayo Clinic Laboratories and by UK laboratories; it is not a narrower optimal target. Lower limits differ between laboratories (20 at Labcorp, 23 on MedlinePlus), so a result of 20 to 22 may be in range on the report. A sample that waits before analysis loses CO2 and reads falsely low.
Sources
- HCO3 - Bicarbonate, Serum — Mayo Clinic Laboratories Test Catalog, 2026 · Laboratory / reference-interval sourceReference values are 22 to 29 mmol/L for men from 18 years and women from 10 years. Matches both edges of Sera's band exactly. Current catalogue entry, opened October 2026.
- Bicarbonate — Worcestershire Acute Hospitals NHS Trust, Pathology tests A to Z, 2026 · Laboratory / reference-interval sourceReference range over 16 years is 22 to 29 mmol/L, attributed to the UK Pathology Harmony ranges. Matches both edges of Sera's band exactly. The page is undated.
- CO2 blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal range is 23 to 29 mEq/L, the same in mmol/L. Matches Sera's upper edge of 29 exactly; the lower limit is 1 above Sera's 22.
- Carbon Dioxide, Total — Labcorp Test Directory, 2026 · Laboratory / reference-interval sourceRange over 12 years is 20 to 29 mmol/L. Matches Sera's upper edge of 29; the lower limit is 2 below Sera's 22, so a result of 20 or 21 may be printed as normal on a Labcorp report. Current directory entry, opened October 2026.
What Bicarbonate (CO2 / Total CO2) measures
The blood's main buffer against acid, managed by the kidneys and lungs together. On US and Gulf panels it is usually printed as CO2 or Total CO2, which means this test and nothing respiratory.
A low bicarbonate is a reason to look at kidney function rather than something to treat on its own, and a high one usually points at fluid loss, vomiting, or certain medicines. Bicarbonate also falls in samples that sit uncapped or are processed late, because it escapes into the air, so a single low result is worth repeating before it means anything.