Glucose
The amount of sugar in your blood at the time of the draw, usually measured fasting.
| Typical reference range | 65–99 mg/dL |
| Commonly cited optimal range | 72–90 mg/dL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Glucose is the body's primary fuel. Blood levels are tightly regulated by insulin (which lowers glucose) and glucagon, cortisol and adrenaline (which raise it). The liver releases glucose overnight to keep fasting levels stable.
Why it matters
Fasting glucose screens for prediabetes (100-125 mg/dL) and diabetes (126 mg/dL or higher on two occasions). Because insulin can keep glucose normal for years while insulin resistance develops, fasting glucose is a late marker and is best read alongside HbA1c and insulin.
What a high result can mean
High fasting glucose suggests insulin resistance, prediabetes or diabetes. It can also be raised temporarily by not fasting, acute stress or illness, poor sleep, corticosteroids, thiazide diuretics, some antipsychotics and, in some people on very low-carbohydrate diets, physiological insulin resistance.
What a low result can mean
Low glucose (below ~70 mg/dL) can result from prolonged fasting, intense exercise, excess diabetes medication, alcohol, adrenal insufficiency or, rarely, insulin-producing tumors. Delayed processing of the sample can also falsely lower results.
What affects the result
Fast 8-12 hours (water is fine). Dawn phenomenon, stress, poor sleep and illness can raise morning readings. Exercise, weight loss, sleep, fiber and limiting refined carbohydrates improve it. Interpret with HbA1c, fasting insulin and HOMA-IR; continuous glucose monitoring gives more detail.
Units and conversion
Usually reported in mg/dL.
- From mmol/L: multiply by 18.016 to get mg/dL
Also called on lab reports
Glucose, Fasting, Fasting Glucose, Glucose, Serum, Glucose, Plasma, Blood Glucose, Fasting Blood Sugar, Blood Sugar, FBS
Related tests: Glucose & Metabolic
This page is educational and does not replace advice from a healthcare professional.