The short answer
For adults without diabetes, using the American Diabetes Association (ADA) criteria:
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting blood sugar (no food for 8 hours) | Below 100 mg/dL (below 5.6 mmol/L) | 100 to 125 mg/dL (5.6 to 6.9 mmol/L) | 126 mg/dL or above (7.0 mmol/L or above) |
| 2 hours after a glucose drink (OGTT) | Below 140 mg/dL (below 7.8 mmol/L) | 140 to 199 mg/dL (7.8 to 11.0 mmol/L) | 200 mg/dL or above (11.1 mmol/L or above) |
| HbA1c (average over about 3 months) | Below 5.7% (below 39 mmol/mol) | 5.7% to 6.4% (39 to 47 mmol/mol) | 6.5% or above (48 mmol/mol or above) |
| Random blood sugar | 200 mg/dL or above (11.1 mmol/L), with symptoms |
Some countries, including the UK and others following the WHO, define prediabetes slightly differently, for example a fasting range starting at 6.1 mmol/L and an HbA1c range of 42 to 47 mmol/mol (6.0% to 6.4%). The diabetes thresholds are the same.
Units: to convert mg/dL to mmol/L, divide by 18.
What each test measures
- Fasting blood sugar: your glucose level after at least 8 hours without food or drinks other than water. It shows how well your body manages sugar overnight.
- Oral glucose tolerance test (OGTT): you drink a measured sugar solution, then blood is tested two hours later. It shows how well your body clears sugar after a load.
- HbA1c: measures how much glucose has attached to your red blood cells, reflecting your average level over about two to three months. No fasting is needed. It can be less accurate with some forms of anaemia, recent blood loss, pregnancy and certain haemoglobin variants.
After-meal readings in people without diabetes
Blood sugar naturally rises after eating, especially after carbohydrate-rich meals. In people without diabetes, it typically peaks within an hour and comes back down to below about 140 mg/dL (7.8 mmol/L) within two hours. Short spikes are normal. Readings from continuous glucose monitors in healthy people vary more than many expect, so do not worry about single numbers in isolation.
Typical targets for people with diabetes
For many non-pregnant adults with diabetes, the ADA suggests:
| Measure | Typical target |
|---|---|
| Before meals | 80 to 130 mg/dL (4.4 to 7.2 mmol/L) |
| 1 to 2 hours after starting a meal | Below 180 mg/dL (below 10.0 mmol/L) |
| HbA1c | Below 7% (53 mmol/mol) for many adults |
| Time in range (with a CGM) | More than 70% of readings between 70 and 180 mg/dL (3.9 to 10.0 mmol/L) |
Targets are individual. Your doctor may set them higher or lower depending on your age, other conditions, risk of low blood sugar and pregnancy. Follow the targets your own care team gives you.
Low blood sugar (hypoglycaemia)
- Below 70 mg/dL (3.9 mmol/L) is generally considered low.
- Below 54 mg/dL (3.0 mmol/L) is significantly low and needs immediate action.
Symptoms: shakiness, sweating, fast heartbeat, hunger, irritability, confusion, blurred vision and, if severe, seizures or loss of consciousness.
Low blood sugar mostly affects people taking insulin or certain diabetes tablets (such as sulfonylureas). A common treatment rule is 15 grams of fast-acting sugar (such as glucose tablets or a small glass of juice), then recheck after 15 minutes and repeat if still low. If someone is unconscious or cannot swallow, call emergency services.
What to do with your result
- Normal: keep up healthy habits. Many health services suggest regular screening from about age 35 to 45, or earlier if you have risk factors.
- Prediabetes range: this is a valuable warning. Losing about 5 to 7 percent of body weight, being active for around 150 minutes a week, and eating more fibre and fewer sugary drinks and refined carbohydrates can substantially reduce the chance of developing type 2 diabetes. Our guides to calorie needs and BMI are useful starting points.
- Diabetes range: see a doctor to confirm the result with a repeat test and discuss treatment. Diagnosis usually needs two abnormal results.
Risk factors for type 2 diabetes
- Being over 40 (over 25 for people of South Asian heritage in some guidelines).
- Excess weight, especially around the waist.
- A parent or sibling with diabetes.
- South Asian, Black African, African-Caribbean, Hispanic or Middle Eastern heritage.
- High blood pressure or a history of gestational diabetes.
- Physical inactivity.
Symptoms of high blood sugar
Many people have no symptoms for years. When they occur, they include frequent urination, strong thirst, tiredness, blurred vision, slow-healing cuts, and unexplained weight loss. See a doctor if you notice these.
Key takeaways
- Normal fasting blood sugar is below 100 mg/dL (5.6 mmol/L).
- HbA1c of 5.7% to 6.4% is prediabetes; 6.5% or above suggests diabetes.
- Targets for people with diabetes are individual; follow your care team's advice.
- Prediabetes can often be reversed with weight loss and regular activity.
This article is general information, not medical advice. Speak to a doctor about your own blood sugar results.