Blood Glucose – A Brief Guide

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Blood Glucose - Our Brief Guide

Blood glucose is the main sugar found in your blood. It is carried throughout the body to supply energy. While it's normal for blood glucose levels to fluctuate, these changes can cause severe problems in people with diabetes, who do not produce enough insulin to keep blood sugar in check. 

On this page you will find information on blood glucose, who needs to monitor it, and how to check blood glucose levels.  

What is Blood Glucose?

Blood glucose, also called blood sugar, comes from the food and drink you consume. It is your body’s main source of energy.  

Diabetes is a condition that occurs when your blood glucose is too high. This can happen when your body does not produce enough insulin — the hormone that controls your blood sugar — or when it doesn’t use it well. Over time, having too much glucose in your blood can cause health problems.  

Though there is no cure for diabetes, there are many ways to manage this condition. Regularly checking blood glucose levels is one of the essential parts of treating diabetes. 

There are two types of diabetes. Type 1 diabetes occurs when the body’s own immune system attacks the cells that produce insulin. Type 2 diabetes is when the body cannot use its insulin supply properly or stops producing it well enough. 

The main symptoms of having high blood glucose due to diabetes include: 

  • going to the toilet a lot, especially at night 
  • feeling exceptionally thirsty 
  • fatigue 
  • unintentional weight loss 
  • genital itching or thrush 
  • cuts and wounds that take longer to heal 
  • blurred vision 

Who Needs to Monitor their Blood Glucose?

If you have diabetes, it is especially vital to keep your blood glucose levels within a target range. Monitoring your blood glucose levels multiple times a day is the best way to keep track, and can give you a sense of what makes your numbers go up and down.  

This can help you plan your day accordingly, because certain foods, exercise, stress and medication will affect your blood glucose levels in different ways.  

Regularly monitoring blood glucose levels will also help avoiding ‘hypos’ which happens when your blood sugar dips dangerously low and can affect people with diabetes, especially those who take insulin. 

How do I Check my Blood Glucose?

There are multiple tests you can do in order to check your blood glucose. Some you can do yourself and others are done in a lab or clinic. 

  • Finger-pricking: You can use a blood glucose meter to check your blood sugar yourself. This device uses a small drop of blood from your finger to measure your blood sugar level. You can get a meter, and more information on how to use it, from your healthcare team. 
  • The HbA1c test: This is a blood test that tells you and your doctor your average glucose levels over the past 2 or 3 months. This test should be done at least once a year. 
  • Urine test: Your GP can also arrange a urine test in order to detect glucose as well as ketones. Testing ketones is important because the body produces this chemical when blood sugar levels rise abnormally high. Having high ketone levels can have serious health risks.  

Results and Target Ranges

Target results will vary individually based on age and the type of diabetes. According to the National Institute for Clinical Excellence (NICE), ‘normal’ blood glucose levels are as follows: 

  • within 4.0 to 5.4 mmol/L (72 to 99 mg/dL) while fasting 
  • up to 7.8 mmol/L (140 mg/dL) 2 hours after eating 


For people with diabetes, blood sugar level targets are as follows: 

  • 4 to 7 mmol/L for people with type 1 or type 2 diabetes (before meals) 
  • under 9 mmol/L for people with type 1 diabetes and under 8.5mmol/L for people with type 2 diabetes (after meals) 

What are the Differences between CGM and Flash Glucose Monitoring?

The chief difference between CGM and flash glucose monitoring is that you must remember to scan your sensor to access your blood sugar levels with Flash.  

With continuous glucose monitors, you can set up alarms to alert you when your blood sugar goes too high or too low. You can programme alarms for the Freestyle Libre 2 as well, but the original Freestyle Libre does not have alarms. 

Another key difference is that Flash is a standalone glucose monitoring system. This means it does not currently integrate with any insulin pumps. CGM devices can either be standalone or paired with compatible insulin pumps. 

Finally, CGM requires that you finger-prick twice per day to calibrate the sensor. Flash does not require calibration. 


For more information on the differences between Flash and CGM, read our guide here.

Living with Diabetes

Living with diabetes can be challenging and it may take some time to understand what your blood glucose levels mean and how to monitor them.  

An experienced, specialised healthcare professional can develop a treatment plan to ensure your blood glucose stays within the target range. 

Looking to speak with a member of our team?

Carol Willis

Carol Willis - Diabetes Clinic Facilitator

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