A blood glucose test is included in virtually every routine check-up — and for good reason. It's the primary screening tool for diabetes and prediabetes, conditions that affect hundreds of millions of people worldwide, often without symptoms.
If your fasting glucose came back slightly elevated, here's what it means and what to do next.
What Is Blood Glucose
Blood glucose is the amount of sugar (glucose) circulating in your bloodstream. Glucose is the body's primary fuel — it comes from food, is absorbed in the intestines, and delivered to every cell via the bloodstream.
Levels are regulated by insulin, a hormone produced by the pancreas. When this regulation breaks down, blood sugar rises (hyperglycemia) or falls (hypoglycemia).
On lab reports, it appears as Glucose or GLU.
Normal Blood Glucose Levels
Results are interpreted differently depending on when blood was drawn:
| Group | Fasting (mmol/L) | 2 hrs after meal |
|---|---|---|
| Adults (normal) | 3.9–5.5 | below 7.8 |
| Prediabetes | 5.6–6.9 | 7.8–11.0 |
| Diabetes | ≥ 7.0 | ≥ 11.1 |
| Pregnancy (gestational) | ≥ 5.1 | ≥ 10.0 |
| Children under 14 | 3.3–5.5 | — |
Reference ranges vary slightly between labs — always check your specific report.
Causes of High Blood Glucose (Hyperglycemia)
- Type 1 diabetes — the pancreas produces little or no insulin
- Type 2 diabetes — cells become resistant to insulin; the most common type
- Prediabetes — borderline levels, often reversible with lifestyle changes
- Gestational diabetes — elevated glucose during pregnancy
- Stress or acute illness — cortisol temporarily raises blood sugar
- Medications — corticosteroids, some diuretics, antipsychotics
- Endocrine disorders — Cushing's syndrome, acromegaly, hyperthyroidism
Causes of Low Blood Glucose (Hypoglycemia)
- Insulin or medication overdose — in people with diabetes
- Prolonged fasting — glucose depleted faster than it's replaced
- Intense physical activity — muscles rapidly consume sugar
- Alcohol — impairs the liver's ability to produce glucose
- Insulinoma — a rare pancreatic tumour that overproduces insulin
- Severe liver disease — impaired glucose synthesis
Symptoms of Abnormal Glucose
When high (hyperglycemia): excessive thirst, frequent urination, dry mouth, fatigue, blurred vision, slow wound healing. With prolonged elevation: numbness in feet, kidney problems.
When low (hypoglycemia): trembling, sweating, rapid heartbeat, hunger, irritability, dizziness, confusion. Severe hypoglycemia can cause loss of consciousness — a medical emergency.
How to Prepare for the Test
- Fast for 8–12 hours before the blood draw — water only
- Avoid alcohol for 24 hours beforehand
- Do not change your normal diet 2–3 days before the test
- Tell your doctor about all medications, especially hormones and diabetes drugs
Blood Glucose vs HbA1c: What's the Difference
Both tests are commonly ordered together when diabetes is suspected:
| Test | What it reflects | Best used for |
|---|---|---|
| Fasting glucose | Sugar level at the moment of the blood draw | Screening, acute diagnosis |
| HbA1c | Average blood sugar over the past 2–3 months | Diabetes monitoring, diagnosis |
If fasting glucose is normal but symptoms are present, a doctor may also order a glucose tolerance test and HbA1c.
When to See a Doctor
See a GP or endocrinologist if:
- Fasting glucose is above 6.1 mmol/L, even once
- Result falls in the prediabetes range (5.6–6.9) and you have excess weight or a family history of diabetes
- You have symptoms: thirst, frequent urination, fatigue, blurred vision
- Glucose is below 3.5 mmol/L, especially with hypoglycemia symptoms
Understand Your Glucose Result in Seconds
A single glucose reading is just the starting point. For a complete picture, it should be assessed alongside other biochemical markers.
Upload your report to LabReadAI — AI will explain what your glucose level means, compare it with age-appropriate norms, and tell you whether an endocrinologist appointment is warranted.