RBC selenium 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 RBC selenium:
- Optimal 120 – 180 ng/mL (120 – 180 μg/L); sufficient 80 – 220 ng/mL (80 – 220 μg/L); out of range below 80 or above 220 ng/mL.
Evidence grade: Functional / longevity target. A narrower target in common use in functional, integrative, preventive and longevity practice. It is not a universally validated diagnostic range.
At Sera's last range review a change to this band was proposed and held, because the evidence for it was thin, so the band is unchanged. The note below says where it matches published intervals and where it does not.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| ng/mL | 120 – 180 | 80 – 220 | below 80 or above 220 |
| μg/L | 120 – 180 | 80 – 220 | below 80 or above 220 |
| μmol/L | 1.52 – 2.28 | 1.01 – 2.79 | below 1.01 or above 2.79 |
What the evidence says
Red cells take up selenium only while they are being made, so this reads the last 120 days where the serum value reads the last few weeks and moves with inflammation. The bands sit ABOVE the serum ones because red cells concentrate selenium. The optimal band is Sera's own derivation and not a published interval: the serum functional target (110–150 ng/mL) multiplied by an assumed RBC:serum ratio of 1.2 to 1.6, for which no published source was found. The one mainstream laboratory interval for red cell selenium is Quest Diagnostics' 120 to 300 μg/L, and the acceptable band here (80 to 220) does not match it: a result of 80 to 119 reads Sufficient here though it is below that laboratory's lower limit, and 221 to 300 reads Out of range though the laboratory calls it normal. Whole blood is a different measurement and is not mapped onto these bands.
Assay: Results differ meaningfully between platforms and methods. Compare against the interval printed by the issuing laboratory before acting on a borderline value.
Sources
- Selenium, RBC — Quest Diagnostics, 2026 · Laboratory / reference-interval sourceReference range 120 to 300 µg/L for red-cell selenium by ICP-MS (test code 17133). The lower limit matches Sera's optimal lower edge of 120; it is 40 above Sera's sufficient lower edge of 80 and the upper limit is 80 above Sera's 220.
- Selenium, Blood — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceWhole-blood selenium reference values for adults 150 to 241 ng/mL. Context only: whole blood is a different specimen, and this interval does not match the 80 to 220 that Sera's note says the sufficient band was aligned with.
What Selenium (RBC) measures
Erythrocyte selenium, the intracellular fraction. Red cells take up selenium only while they are being made, so this reflects status over the 120-day lifespan of the cell rather than the last few weeks.
The reason to measure it: serum selenium moves with recent intake and with inflammation, so it answers a different question from the one a practitioner usually has. Worth measuring when the serum value is borderline, or when chronic deficiency or accumulation is suspected. Read it alongside the serum value where both exist — neither replaces the other. Whole-blood selenium is a third matrix again, mixing plasma with red cells, and is not interchangeable with this.