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Blood and plasma glucose

Blood and plasma glucose

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 2 diabetes can have blood glucose levels that are too high (called hyperglycaemia).

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

  • eat more food than your body needs

  • do not take your metformin

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

Blood glucose is measured in mmol/litre (this means the millimoles of glucose in every litre of your blood or plasma). 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).

Plasma glucose

Instead of 'blood glucose', your diabetes team might speak about 'plasma glucose'. Plasma is the liquid portion of your blood. It is mainly made of water. Plasma glucose is the sugar in your plasma. Measuring plasma glucose instead of blood glucose is just a different way of measuring the amount of sugar in your blood. Plasma glucose, like blood glucose, is measured in mmol/litre.

Questions to ask about blood glucose

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

HbA1c

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%).

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, and help you reach it.

Your diabetes team should check your HbA1c level every 3 months. They do this with a finger‑prick test.

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 keep my HbA1c at the level I'm aiming for?

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

Checking your glucose levels

Self-monitoring

You should check your blood or plasma glucose level regularly with a finger-prick home‑testing kit. This is called self-monitoring. How often you do it depends on:

  • the medicines you are taking for your diabetes

  • how stable your blood or plasma glucose levels are.

Your diabetes should give you the testing kit you will need and explain how to use it. They will also discuss how often you will need to test.

Questions to ask about self-monitoring

  • How often should I do a finger-prick test?

Continuous glucose monitoring

You might also be offered something called continuous glucose monitoring, or CGM for short. CGM is done by wearing a device that checks your blood glucose automatically for you, at regular intervals.

You should be offered this if you:

  • have a need, condition or disability (including a mental health need, learning disability or cognitive impairment) that means checking your glucose levels in another way would be difficult for you

  • would otherwise be advised to test yourself at least 8 times a day

  • have hyperglycaemia often or repeatedly, or

  • have severe hypoglycaemia.

You might also be offered CGM if you are taking a medicine called insulin for your diabetes.

If you are offered CGM:

  • your diabetes team should discuss the options with you, and help you choose a device that will work for you

  • you should wear your device as often as possible.

If you use a CGM device, you will still need to self-monitor, but less often. This is so that you can check that your CGM device works well and to use as back-up if your device stops working.

Questions to ask when choosing a CGM 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?

  • 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?

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