Biomarker · Metabolic
Fasting blood glucose
Fasting blood glucose measures sugar in your blood after an overnight fast. Learn how it's used to screen for prediabetes and diabetes and what can affect it.
Written by LON6EVITY Editorial Team · Last updated
Overview
Fasting glucose is the concentration of glucose in the blood after not eating for at least 8 hours.
Why it matters
It is one of the standard tests used to screen for prediabetes and diabetes. Unlike HbA1c, it reflects a single point in time.
Higher and lower results
Higher fasting glucose can reflect insulin resistance, diabetes, stress, illness or some medications. Low glucose (hypoglycaemia) can cause symptoms such as shakiness and confusion and needs medical attention if recurrent.
How the test is performed
Blood is drawn in the morning after an 8-hour fast. Water is normally allowed.
Reference ranges
| NIDDK: normal | < 100 mg/dL (< 5.6 mmol/L) |
|---|---|
| NIDDK: prediabetes range | 100–125 mg/dL (5.6–6.9 mmol/L) |
| NIDDK: diabetes range | ≥ 126 mg/dL (≥ 7.0 mmol/L) |
Reference ranges and targets differ between laboratories, units and guidelines, and depend on age, sex, method and your overall clinical picture. A single result is not a diagnosis — interpret it with a qualified clinician.
Factors that can affect the result
- Not fasting
- Acute illness or stress
- Corticosteroids and other medications
- Poor sleep
Questions people commonly ask
- Is one high fasting glucose a diagnosis of diabetes?
- No. Diagnosis normally requires confirmation with a repeat test or a different test, interpreted by a clinician.
Related biomarkers
Related tests
Related topics
Understand your biomarkers in context
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- Blood Glucose Test. MedlinePlus, U.S. National Library of Medicine.
- Diabetes Tests & Diagnosis. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).