Medical test · Diabetes & glucose
Blood glucose
Also known as: blood sugar, plasma glucose
The concentration of glucose in blood, measured from a vein or a fingerprick. Fasting, random and after-a-sugar-drink (oral glucose tolerance) versions answer different questions.
- Kind
- Laboratory test
- Categories
- Diabetes & glucose, Chemistry & metabolic
- Specimen
- Serum or plasma, Capillary (fingerprick) blood
- Method
- Chemistry analyser, Point-of-care device
- Terminology
- LOINC 2345-7, 1558-6
What it measures
| Measure | What it tells you |
|---|---|
| Fasting glucose | After 8 hours without food; normal below 5.6 mmol/L, diabetes at 7.0 or above on two occasions. |
| Random glucose | Any time of day; 11.1 mmol/L or above with symptoms suggests diabetes. |
| Oral glucose tolerance | Glucose two hours after a 75 g drink; used in pregnancy and borderline cases. |
Why it is ordered
- Thirst, passing lots of urine, weight loss
- Screening for diabetes in people at risk
- Confusion, sweating or collapse (hypoglycaemia)
- Monitoring insulin and other diabetes treatment
How it is done
Venous sample in a fluoride tube, or a capillary fingerprick on a meter; continuous glucose monitors sample fluid under the skin.
Preparation. Fasting tests need 8-12 hours without food, water allowed.
Reading the result
| Finding | Usual meaning |
|---|---|
| Fasting 5.6-6.9 mmol/L | Impaired fasting glucose: prediabetes, a chance to change course |
| Fasting 7.0 or above | Diabetes if repeated or with symptoms |
| Below 4.0 mmol/L | Hypoglycaemia: usually insulin or sulfonylurea excess; treat with fast sugar |
Reference ranges vary by laboratory, method, age, sex and clinical context; a result is read against the person, not a table.
Limitations
A single value is a snapshot; HbA1c gives the three-month average. Stress and illness raise glucose temporarily.
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.
Educational content. Reference ranges differ between laboratories, methods, ages and sexes, and results are always read against the person, the question asked and other findings. This page cannot interpret an individual result.