Fasting Glucose (Blood Sugar)
Fasting blood glucose measures the amount of sugar in your blood after at least 8 hours without food. It is the simplest and most widely used test for screening and diagnosing diabetes. Unlike HbA1c, which reflects a 2–3 month average, fasting glucose is a snapshot of how well your body regulates sugar at a specific moment.
Normal Range
Normal: 70–99 mg/dL fasting; 100–125 pre-diabetes; ≥126 diabetes (on two tests)
Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.
Why is Glucose measured?
Fasting glucose is ordered to screen for and diagnose pre-diabetes and type 2 diabetes, monitor existing diabetes, evaluate symptoms of high sugar (thirst, frequent urination, unexplained weight loss) or low sugar (shakiness, sweating, confusion), and assess metabolic syndrome.
High Glucose means…
A fasting glucose of 100–125 mg/dL is pre-diabetes; 126 mg/dL or higher on two separate tests confirms type 2 diabetes. Persistently high glucose damages blood vessels, nerves, kidneys, and eyes over time.
Low Glucose means…
Below 70 mg/dL is hypoglycaemia. Mild hypoglycaemia is common in people on insulin or sulphonylureas; severe hypoglycaemia (below 54 mg/dL) is dangerous and can cause loss of consciousness or seizures.
Symptoms associated with abnormal Glucose
When Glucose is high:
- Increased thirst and frequent urination
- Unexplained fatigue
- Blurred vision
- Slow-healing cuts
- Recurrent infections
When Glucose is low:
- Shakiness, trembling, or weakness
- Cold sweats
- Confusion or difficulty concentrating
- Hunger
- Rapid heartbeat
- Dizziness or fainting in severe cases
How to improve your Glucose
- Avoid simple carbohydrates and sugary drinks — choose whole grains, vegetables, and protein-rich meals.
- A 30-minute brisk walk after meals can reduce post-meal glucose spikes by 20–30%.
- Adequate sleep (7–9 hours) helps insulin sensitivity — sleep loss raises blood sugar the next day.
- If you take diabetes medication, always carry fast-acting glucose (juice or glucose tablets) in case of hypoglycaemia.
- A 5–7% body weight loss can normalise pre-diabetic glucose values in many people.
Frequently asked questions about Glucose
What is a normal fasting blood sugar?
For non-diabetic adults, a normal fasting blood sugar is 70–99 mg/dL (3.9–5.5 mmol/L). Values of 100–125 indicate pre-diabetes, and 126 or above on two tests confirms diabetes.
Why does fasting glucose differ from HbA1c?
Fasting glucose captures one moment in time, while HbA1c reflects average glucose over 2–3 months. People with normal fasting glucose can still have elevated HbA1c if they spike high after meals — a pattern your doctor calls 'post-prandial hyperglycaemia'.
How long should I fast before the test?
Most labs require 8–12 hours without food or caloric drinks. Water, black coffee, and tea (no milk or sugar) are usually fine but check with your lab.
Medical Sources
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.