Fasting Insulin 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 Fasting Insulin:
- Optimal 3 – 8 μIU/mL (21 – 56 pmol/L); sufficient 2 – 20 μIU/mL (14 – 139 pmol/L); out of range below 2 or above 20 μIU/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 |
|---|---|---|---|
| μIU/mL | 3 – 8 | 2 – 20 | below 2 or above 20 |
| pmol/L | 21 – 56 | 14 – 139 | below 14 or above 139 |
| mIU/L | 3 – 8 | 2 – 20 | below 2 or above 20 |
What the evidence says
No guideline sets a fasting insulin threshold, and assays are not standardised against each other. The acceptable band of 2 to 20 μIU/mL sits between two laboratory intervals and matches neither: Labcorp prints 2.6 to 24.9. The optimal band of 3 to 8 is a functional target with no cohort or society source behind either edge.
Assay: Results differ meaningfully between platforms and methods. Compare against the interval printed by the issuing laboratory before acting on a borderline value.
Sources
- Insulin — Labcorp, 2026 · Laboratory / reference-interval sourceReference range for fasting insulin is 2.6 to 24.9 μIU/mL on Labcorp's Roche assay. Sera's sufficient band of 2 to 20 is narrower at the top and wider at the bottom. Page carries no date; opened October 2026.
What Fasting Insulin measures
Your insulin level after not eating, usually overnight.
High insulin is a sign of insulin resistance, often years before blood sugar starts to rise.