Explainer · updated 2026-09-09

Glucose, explained in plain English

Written by the medk.AI team · Last reviewed September 2026 by the medk.AI content team

Key facts

• Typical adult fasting reference interval: 70-99 mg/dL (ABIM)
• The same fasting interval in mmol/L (converted from the ABIM range): 3.9-5.5 mmol/L (ABIM)
• Level below which glucose is classed as hypoglycaemia: 70 mg/dL (ADA 2026)
• What the test measures: the sugar your cells run on, measured in the fluid part of the blood after a period without food (ADA 2026)

What it is

Glucose is the sugar your cells run on. The number on your report is glucose measured in the fluid part of the blood, usually from a sample taken after a period without food. It is one of the results doctors read when deciding whether diabetes is present, and it moves within minutes of a meal.

What the number is telling you

Because glucose moves quickly, context carries the meaning: whether the sample was fasting, how long since you last ate, and what your previous results look like. One reading says little; time and trend matter.

What high or low can mean

High: A fasting level above the diagnostic cut-off on two separate occasions meets the definition of diabetes. A level between the raised cut-off and the diagnostic cut-off is prediabetes, a warning zone below the diabetes line. Where your own level sits is for your doctor to say.

Low: Below 70 mg/dL is hypoglycaemia, blood sugar that has run low. It matters most in people on insulin or on the older diabetes tablets, because those are the treatments that can push glucose down.

What a typical result looks like

Typical adult fasting reference intervals from ABIM run from 70 to 99 mg/dL, about 3.9 to 5.5 mmol/L. The range on your own report is the one that counts.

Questions worth asking your doctor

• Was this a fasting sample, and does that change how it reads?
• How does this compare with my previous results?
• If my level was high, does it need to be repeated before it means anything?
• If my level was low, could any medicine I take be responsible?

If a result worries you, ask your doctor.

Sources

• ABIM Laboratory Test Reference Ranges (2026)
• Standards of Care in Diabetes 2026, American Diabetes Association (2026)