Fasting Glucose 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 Glucose:
- Optimal 70 – 85 mg/dL (3.9 – 4.7 mmol/L); sufficient 70 – 99 mg/dL (3.9 – 5.5 mmol/L); out of range below 70 or above 99 mg/dL.
Evidence grade: Established clinical threshold. A band edge that corresponds to a recognised diagnostic, risk or treatment threshold from a major clinical guideline or public-health body.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mg/dL | 70 – 85 | 70 – 99 | below 70 or above 99 |
| mmol/L | 3.9 – 4.7 | 3.9 – 5.5 | below 3.9 or above 5.5 |
What the evidence says
The acceptable band stops at 99 mg/dL (5.5 mmol/L), immediately below the ADA's impaired-fasting-glucose threshold of 100 mg/dL (5.6 mmol/L). The line is not the same everywhere: NICE in the UK counts 5.5 to 6.9 mmol/L as high risk, and Diabetes Canada does not call fasting glucose impaired until 6.1 mmol/L. The lower edge of 70 mg/dL (3.9 mmol/L) is the usual laboratory lower limit and the conventional definition of low blood sugar. The narrower optimal band ending at 85 mg/dL is a practitioner target, not a guideline figure; no current guideline or recent cohort study sets it.
Sources
- Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026 — American Diabetes Association Professional Practice Committee — Diabetes Care, 2026 · Clinical guidelinePrediabetes by fasting glucose is 100 to 125 mg/dL (5.6 to 6.9 mmol/L). Sera's sufficient band stops at 99 mg/dL, just below it. Current edition in force.
- Diabetes Testing — Centers for Disease Control and Prevention, 2024 · Government / public-health guidanceFasting blood sugar: normal is 99 mg/dL or below, prediabetes 100 to 125, diabetes 126 or above. Matches Sera's sufficient upper edge.
- Glucose — Labcorp, 2026 · Laboratory / reference-interval sourceReference range 70 to 99 mg/dL, the same two numbers as Sera's sufficient band. Page carries no date; opened October 2026.
- Low Blood Sugar (Hypoglycemia) — Centers for Disease Control and Prevention, 2024 · Government / public-health guidanceBlood sugar below 70 mg/dL is called low blood sugar. The page is written for people with diabetes; it is the conventional figure behind Sera's lower edge of 70.
- Type 2 diabetes: prevention in people at high risk (PH38): Recommendations — National Institute for Health and Care Excellence, 2017 · Clinical guidelineA fasting plasma glucose of 5.5 to 6.9 mmol/L indicates high risk of type 2 diabetes; below 5.5 is not high risk. Published 2012, last updated September 2017 and still in force. The NICE line sits 0.1 mmol/L lower than the ADA line, so exactly 5.5 mmol/L is high risk under NICE.
- Definition, Classification and Diagnosis of Diabetes, Prediabetes and Metabolic Syndrome (Chapter 3) — Diabetes Canada Clinical Practice Guidelines Expert Committee (Punthakee Z, Goldenberg R, Katz P), 2018 · Clinical guidelineImpaired fasting glucose is 6.1 to 6.9 mmol/L in Canada, a higher line than the ADA's 5.6. Sera's 5.5 mmol/L is the stricter ADA convention. 2018 is the current full edition.
What Fasting Glucose measures
Your blood sugar level after not eating, usually overnight.
High fasting glucose can be an early sign of insulin resistance or pre-diabetes.