Information for the public

Blood glucose

Blood glucose is the sugar in your blood. Your blood glucose has to be at the right level to keep you healthy, as you can get ill from having blood glucose that is too high or too low. People with type 1 diabetes need to inject insulin to get their blood glucose to the right level.

Lots of things can make your blood glucose levels go higher or lower. For example, your blood glucose levels can get too low if you:

  • inject too much insulin

  • do more exercise than you planned to do

  • do not eat enough food.

Your blood glucose can get too high if, for example, you:

  • do not inject enough insulin

  • exercise when your blood glucose levels are already high

  • are ill (for example, if you have the flu).

When your blood glucose goes too low, this is called hypoglycaemia (or a hypo for short). When your blood glucose goes too high, this is called hyperglycaemia (or a hyper).

Younger children can find out more about hypoglycaemia and hyperglycaemia on the Diabetes UK website.

Checking your blood glucose

You should be offered a real-time continuous glucose monitor (rtCGM) so that you can be aware of your blood glucose level at any time. You and your diabetes team should choose a device together, based on your preferences and needs.

You should be offered an intermittent-scanning continuous blood glucose monitor (isCGM, also called 'flash') if you cannot use rtCGM, or if you prefer isCGM.

Both types of continuous glucose monitor work with a sensor that you wear on your skin, and a display monitor or smartphone that shows your blood glucose level. rtCGM devices automatically send regular readings to the monitor or smartphone. You need to scan isCGM devices yourself.

If you cannot or do not want to use rtCGM or isCGM, you should be offered finger-prick testing to check your blood glucose levels. To do this, you prick your finger to get a drop of blood. You put this blood onto a meter strip, insert the strip into a testing meter, and it tells you your blood glucose levels. If you are using finger-prick testing, it's important to check your blood glucose at least 5 times every day. Sometimes you may need to check it more often (for example, if you are ill, playing sports or doing other exercise, or will be driving that day).

Even if you use continuous glucose monitoring, you will need to do finger-prick tests from time to time (for example, to check that your monitor is accurate). Your diabetes team will explain when you need to do finger-prick tests.

Your diabetes team will show you how to use the device or devices that you choose, and they will make sure you have enough testing strips.

Younger children can find out more about checking blood glucose on the Diabetes UK website.

Questions to ask when choosing an rtCGM or isCGM monitor

  • How accurate is the monitor?

  • Can the monitor alert me when my blood glucose levels become too high or too low?

  • Do I need a smartphone to use the monitor? Do I need to install a specific app?

  • Is the device easy to use?

  • Could this device connect with my insulin pump?

  • Will wearing this device stop me doing any of the things I normally do as part of everyday life?

  • How visible is the device? Can I wear it under my clothes?

Getting your blood glucose to the right level

Your diabetes team will help you manage your diabetes and get your blood glucose to the right level. They will help you decide:

  • how much insulin you need

  • when you should inject your insulin

  • what kind of insulin works best for you

  • how to change the amount of insulin you are injecting, so that you are taking the right amount for your blood glucose levels

  • how much exercise to do

  • what food and drink to eat.

Blood glucose is measured in mmol/litre (this means the millimoles of glucose in every litre of your blood). Millimoles are a unit of measurement, like litres or metres.

It's best to try to get your blood glucose to the level it would be if you did not have diabetes. This stops you getting problems like hypos, or problems that diabetes could cause you in the future (such as eye damage or gum disease). If possible, you should aim to get your blood glucose to these levels:

  • When you wake up and before you have any food, between 4 mmol/litre and 7 mmol/litre.

  • For young people aged 17 and over who are going to drive: at least 5 mmol/litre.

  • Before a meal, between 4 mmol/litre and 7 mmol/litre.

  • After a meal, between 5 mmol/litre and 9 mmol/litre.

You and your diabetes team will agree what level of blood glucose is best for you (your target level). Your target level might be the levels written above, or it might be higher than this. Your diabetes team should help you decide a target level that does not cause you problems (such as hypos), and help you reach it.

Questions to ask about blood glucose

  • Could you show me how to measure my blood glucose?

  • Why do you think I should have target blood glucose levels that are different to the best level?

  • What could happen if I do not keep my blood glucose at my target level?

  • Could you tell me more about how my blood glucose levels and diabetes affect driving?

  • Can you give me any written information? What websites are helpful?

HbA1c

Your blood glucose levels tell you how much glucose is in your blood right now. HbA1c (also called 'glycated haemoglobin') tells you the average amount of glucose that has been in your blood for the last 2 or 3 months.

HbA1c is measured in mmol/mol (millimoles per mole). Millimoles and moles are units of measurement, like litres or metres. HbA1c is also sometimes written as a percentage (for example, 6.5%).

Like with blood glucose, it's best to have an HbA1c level that's as close as possible to the level it would be if you did not have diabetes. This level is 48 mmol/mol or less (this is the same as 6.5% or less). Keeping your HbA1c level under control means you're less likely to get other problems caused by diabetes. Your diabetes team should help you decide a target level that does not cause you problems (such as a lot of hypos), and help you reach it.

Your diabetes team should check your HbA1c level 4 times a year. They do this with a finger‑prick test. If you are having problems with your blood glucose levels, they may check your HbA1c level more often.

When you start injecting insulin for the first time, you may find that you only need a small amount to keep your HbA1c at the right level. This is called a 'honeymoon period'. Over time, you will find that you need more insulin to control your diabetes.

Questions to ask about HbA1c

  • Why do you think I should aim for a HbA1c level that is different to the best level?

  • What could happen if I do not keep my HbA1c at the level I'm aiming for?

  • Can you help me to keep my HbA1c at the level I'm aiming for?

  • Can you give me any written information? What websites are helpful?

  • Information Standard