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Flash glucose monitoring

A flash glucose monitor is a small wearable device that you scan with a reader or mobile phone to check your glucose levels.
Content last reviewed and updated: 04.08.2023

A man using flash glucose monitoring - holding a mobile app and glucose sensor on his arm

What is a flash glucose monitor?

A flash glucose monitor reduces the number of finger prick glucose tests you need to do, and some models alert you when your glucose levels are going too high or too low. Flash can be a good way to measure your levels more easily and frequently than with blood glucose meters alone, and shows if your glucose is rising, falling or level.

A flash glucose monitor is often known by its brand name, Freestyle Libre. If you hear people talking about Libre or Libre 2, it’s the same as flash and flash 2 (more on these further on).

How does flash glucose monitoring work?

You attach a sensor, which is about the size of a £2 coin, to the upper arm and keep this on for up to 14 days. A filament from the sensor sits under the skin to measure how much glucose there is in the fluid between blood vessels and cells (this is called interstitial fluid).

This filament is put in place with a needle which is then retracted back into the inserter. It all happens in an instant – all you need to do is press a button.

When you want to check your glucose levels, you scan or ‘flash’ your sensor with a handset or compatible mobile phone to get a reading.

The reading gives you:

  • your current glucose level
  • a graph of your glucose level over the last eight hours
  • a trend arrow to show if your blood glucose is rising, stable or falling

You can review your glucose data on the handset or use a cloud-based platform on your mobile phone or computer. This allows you to see trends in your glucose levels or share your data with your healthcare team.

With the original flash (also known as the Libre), it is recommended that you still verify low glucose readings with a finger prick measurement. With any flash model it’s recommended that you check any rapidly changing glucose readings or any readings which don’t match your symptoms.

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What are the different types of flash glucose monitors?

The original Flash (also known as Libre) works as outlined above. It is also the one that has been most widely available on the NHS but is gradually being phased out and replaced with Flash 2.

Flash 2 (also known as Libre 2) has slightly more advanced functions and is increasingly offered by Diabetes Healthcare Teams. With flash 2, you can set optional personalised alarms which prompt you to scan for a reading when your glucose levels are out of target range. The accuracy of flash 2 has been improved so you don’t have to check readings by doing a finger prick test as often.

What is the difference between a flash glucose monitor and a continuous glucose monitor?

The main difference between continuous glucose monitor (CGM) and flash is that a CGM transmits data to your phone or handset all the time. A flash glucose sensor only gives you a reading when you scan – or ‘flash’ – the sensor with your phone or handset.

However, the FreeStyle Libre 3 has evolved to become a CGM, giving you constant, real-time glucose readings and the option to set alarms for high and low glucose levels.

Do flash glucose monitors work with other tech?

No, flash glucose monitors aren’t compatible with other tech, like insulin pumps. If you want to integrate your glucose measurement with your insulin intake, visit our guides on CGM or hybrid closed loop technology.

What sensors are available?

The only flash sensors that are available are the FreeStyle Libre (Flash) and Libre 2 (Flash 2). 

How much does a flash glucose monitor cost?

Flash sensors cost around £50 each and last for up to 14 days.

Can I get a flash glucose monitor on the NHS?

Flash should be available on the NHS to anyone with type 1, but it can still depend on where you live. Find out whether you can access flash on the NHS in England and Wales, Scotland and Northern Ireland.

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