Fasting Blood Sugar
A blood test that measures sugar (glucose) after not eating for at least 8 hours.
Quick Summary
To screen for and diagnose diabetes and prediabetes, and to monitor treatment.
Blood glucose after fasting.
Fast for 8–10 hours (water is allowed). Take medicines as advised.
Overview
Fasting sugar shows how well your body controls sugar without food.
It's often done with post-meal sugar or HbA1c.
What It Measures
Fasting glucose
Sugar level after an overnight fast.
How It's Performed
- 01
Preparation
Fast (nothing to eat or drink except water) for the time your lab advises, usually 8–12 hours.
- 02
Blood sample
A small amount of blood is taken from a vein in your arm with a thin needle.
- 03
Afterwards
Press on the spot for a minute. A small bruise is common; you can go back to normal activities.
Reference Ranges
Note: Normal ranges vary by laboratory. Consult your report for the specific reference used.
| Parameter | Typical Range (Adult) | Units |
|---|---|---|
| Normal | 70–99 | mg/dL |
| Prediabetes | 100–125 | mg/dL |
| Diabetes | 126 or above (on two tests) | mg/dL |
Interpreting Results & Next Steps
Discuss with Doctor
Normal ranges differ between laboratories, ages and sexes; always use the range printed on your report and ask your doctor what your results mean.
If values are Low:
Low sugar (below about 70) can cause shakiness and confusion.
If values are High:
High fasting sugar suggests prediabetes or diabetes; a repeat test or HbA1c confirms it.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Blood Glucose Test(opens in a new tab) · MedlinePlus, US National Library of Medicine
- Diabetes tests(opens in a new tab) · MedlinePlus, US National Library of Medicine