What is Glucose?
Blood glucose is the main sugar in your blood and your body's primary energy source, tightly regulated by insulin. A fasting glucose test, taken after 8+ hours without eating, is a standard screen for prediabetes and diabetes and a core marker of metabolic health.
Why it matters
Fasting glucose reveals how well your body regulates blood sugar at rest. Elevated fasting glucose is an early sign of insulin resistance and predicts diabetes and cardiovascular disease.
What it measures
The concentration of glucose in serum or plasma, ideally after an 8–12 hour fast.
Reference & optimal ranges
Reference ranges vary by lab, assay, age, and sex. The ranges below reflect commonly published adult intervals and are for education only always interpret results with the range printed on your own lab report and a clinician.
High fasting glucose (hyperglycemia) indicates impaired blood sugar control prediabetes (100–125) or diabetes (≥126).
Common symptoms
- Increased thirst and urination
- Fatigue
- Blurred vision
- Often none in early stages
Potential causes
- Insulin resistance / type 2 diabetes
- Type 1 diabetes
- Stress or acute illness
- Steroids and some medications
- Non-fasting sample
Low glucose (hypoglycemia) can cause acute symptoms and, if severe, is dangerous; most common in people on diabetes medication.
Common symptoms
- Shakiness, sweating
- Hunger
- Confusion, difficulty concentrating
- Palpitations
- Dizziness or fainting
Potential causes
- Diabetes medication (insulin, sulfonylureas)
- Prolonged fasting
- Excess alcohol
- Rare hormone or tumor causes
How to improve your Glucose
Lifestyle
Lose excess weight
Reducing abdominal fat improves insulin sensitivity and lowers fasting glucose.
Nutrition
Limit refined carbs and sugary drinks
Emphasize fiber, protein, and whole foods to steady blood sugar.
Exercise
Regular activity
Both aerobic and resistance exercise improve glucose uptake; a post-meal walk helps immediately.
Sleep
Prioritize sleep
Sleep loss raises fasting glucose and worsens insulin resistance.
Frequently asked questions
Scientific references
- Standards of Care in Diabetes Diagnosis & Classification American Diabetes Association (2025)
- Blood Glucose Test MedlinePlus, U.S. National Library of Medicine
Educational information, not medical advice. This page is for general education and does not replace diagnosis or treatment by a licensed clinician. Do not start, stop, or change any medication, supplement, or treatment based on this content. Reference and optimal ranges vary between laboratories interpret your results with the range on your own report and a qualified professional.