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Continuous glucose monitoring (CGM) and flash

You can check your sugar (glucose) levels at any time with a continuous glucose monitor (CGM) or flash monitor.

It lets you see patterns in your levels and check if your glucose is too high or low. It can help you control your blood glucose levels, as you'll have more information and can take action quickly.

It can help you and your diabetes team see:

  • if your glucose levels are going up or down
  • how your glucose levels change over time
  • what happens to your levels when you're asleep

If your blood glucose reading is:

How it works

A CGM or flash monitor is made up of:

  • a sensor – a small device you attach to your arm or tummy that senses how much glucose is in the fluid under your skin, called interstitial fluid
  • a reader or receiver, which shows the results (you can also get the results on your smartphone, if you have one)

With CGM, the sensor sends results to the receiver or your phone every few minutes. You can see your glucose levels on your receiver at any time. Some types can send results to an insulin pump, so you can see your glucose levels on your pump.

With flash, you need to scan the sensor with the reader or with your phone to see the results.

There are several different types of CGM. The only types of flash monitor available are the Abbott FreeStyle Libre and FreeStyle Libre 2.

Some types of CGM have optional alarms to alert you if your blood glucose levels go too low or too high. The Abbott FreeStyle Libre 2 also has an alarm, but it only sounds when you scan the sensor.

You generally need to replace a sensor every 7 to 14 days, depending on the type of monitor you have.

Interstitial fluid glucose readings are a few minutes behind your blood glucose levels. This means you'll still need to do finger-prick checks every now and then, particularly when you drive or have a hypo.

To get the best out of CGM or flash, you'll need to look at the information it gives you with your team.

Getting CGM or flash on the NHS

CGM or flash glucose monitoring should be available on the NHS to anyone with type 1 diabetes.

Children and young people will usually be offered CGM. Adults will usually be offered a choice of CGM or flash.

Ask your diabetes team about getting CGM or flash glucose monitoring.

Learn more about CGM and flash from Diabetes UK

Page last reviewed: 6 July 2021
Next review due: 6 July 2024