Blood glucose is measured in millimoles per litre (mmol/L) in most countries, or milligrams per decilitre (mg/dL) in the US. Fasting means no food or caloric drink for at least 8 hours. Normal fasting glucose is below 5.6 mmol/L (100 mg/dL); the prediabetes range is 5.6–6.9 mmol/L; 7.0 mmol/L or above on two separate occasions confirms type 2 diabetes.
Why blood sugar levels matter
Glucose is the primary fuel for every cell in your body. When blood sugar stays persistently high, it damages blood vessels, nerves, eyes and kidneys — most of it silently, over years. By the time symptoms appear, significant harm is often already done.
The good news is that both prediabetes and early type 2 diabetes are highly responsive to intervention. Monitoring and understanding your levels is the first step.
The four main blood sugar tests
- Fasting plasma glucose (FPG) — taken after an 8-hour fast; the most common screening test
- HbA1c — reflects average blood sugar over the past 2–3 months; no fasting required
- 2-hour oral glucose tolerance test (OGTT) — measures response to a 75 g glucose drink; most sensitive for prediabetes
- Random plasma glucose — taken at any time; a reading above 11.1 mmol/L with symptoms confirms diabetes
What the numbers mean: a reference table
| Category | Fasting glucose | HbA1c | 2-hr OGTT |
|---|---|---|---|
| Normal | < 5.6 mmol/L (< 100 mg/dL) | < 5.7% | < 7.8 mmol/L |
| Prediabetes | 5.6–6.9 mmol/L (100–125 mg/dL) | 5.7–6.4% | 7.8–11.0 mmol/L |
| Diabetes | ≥ 7.0 mmol/L (≥ 126 mg/dL) | ≥ 6.5% | ≥ 11.1 mmol/L |
Post-meal (postprandial) levels
For people without diabetes, blood sugar typically peaks 1 hour after eating and returns below 7.8 mmol/L (140 mg/dL) by 2 hours. Readings consistently above this threshold after meals — even if fasting levels are normal — can indicate early insulin resistance and are worth discussing with your doctor.
Wearable continuous glucose monitors (CGMs) now let people see their real-time glucose curves without fingerprick testing. If you're using one, aim for a time-in-range above 70% between 3.9–10.0 mmol/L.
What to do if your result is in the prediabetes range
Prediabetes is not a diagnosis to ignore, but it is also not an inevitable path to diabetes. The landmark Diabetes Prevention Program trial showed that structured lifestyle change — 7% body weight loss and 150 minutes of moderate activity per week — reduced progression to type 2 diabetes by 58%, more than medication.
Ask your doctor about a diabetes prevention programme. Track your results over time — HbA1c trends across multiple readings tell a far richer story than any single value.
"A prediabetes diagnosis is one of the most actionable results in medicine. It's a window — and for most people, lifestyle change is enough to close it."
Dr. Lina Haddad, CMO, Looms
Keeping track of your glucose history
Whether you're monitoring after a diagnosis or tracking preventively, uploading your results to a platform like Looms lets you see glucose trends across every test — fasting, HbA1c, OGTT — in one place. A pattern of gradual increase is exactly the kind of signal that gets missed when results are scattered across different labs and appointment summaries.