Last Updated on March 11, 2026 by Williams
Capillary blood glucose (CBG)
Capillary blood glucose (CBG) tests are Blood glucose level (BGL) or Blood sugar level (BSL) monitoring conducted outside of clinical facilities, such as at home. They can also be referred to as self-monitoring blood glucose (SMBG).
CBG is important for diabetics to monitor their blood sugar, which helps determine if they are meeting their glucose targets. This helps them reduce the unpleasant symptoms of high and low blood sugar and avoid long-term diabetes complications.
CBG testing helps people understand their current blood sugar level and how it changes throughout the day. This information supports day‑to‑day diabetes management and helps individuals recognise patterns that may affect their wellbeing
What is a normal CBG level in the UK?
Target blood glucose ranges vary from person to person, but a commonly used reference range for many adults is:
- 4 to 7 mmol/L before meals
- Levels below 4 mmol/L may be associated with symptoms of low blood sugar
- Levels above 8 mmol/L may not cause symptoms but can still be higher than recommended for some individuals
These ranges are general guidelines. A healthcare professional may set different targets based on individual circumstances.
When should I test my CBG?
Testing frequency depends on the type of diabetes, treatment plan, and personal goals. In many cases, people may be advised to check their CBG:
- Before meals
- At bedtime
- When adjusting insulin doses
- When feeling unwell or noticing symptoms of high or low blood sugar
- Before driving, if recommended by a healthcare professional
People using multiple daily insulin injections or insulin pumps may need to test more frequently than those using long‑acting insulin alone
Why it’s important
- CBG tests provide immediate information on blood sugar levels
- This information is important for managing diabetes and other metabolic disorders
- Unusually high or low blood sugar levels can be life-threatening
How CBG testing works
A typical CBG test involves:
- Cleaning the fingertip
- Using a lancet to obtain a small drop of blood
- Applying the blood to a test strip
- Reading the result on a glucose meter
Modern meters provide results within seconds and store readings for later review.
| Method | What it measures | Where it’s used | Notes |
|---|---|---|---|
| CBG (finger‑prick test) | Capillary blood glucose | Home or clinic | Gives a single reading at a specific moment |
| Laboratory plasma glucose | Venous blood glucose | Clinical settings | Used for diagnosis and formal testing |
| Continuous glucose monitoring (CGM) | Interstitial glucose | Worn on the body | Shows trends and alerts; may differ from CBG |