Continuous Glucose Monitoring (CGM)

Continuous Glucose Monitoring is a method of continually measuring the glucose levels within the interstitial fluid.


CGM Explained

  • CGM measures glucose levels throughout the day and night.
  • A CGM system comprises of a Sensor, Transmitter and a hand-held
  • A small electrode known as a glucose sensor is inserted under the skin using an insertion device.
  • The sensor measures the glucose levels in the tissue fluid. (interstitial glucose)
  • Glucose levels in the interstitial fluid lag behind glucose levels in your blood by up to 15 minutes
  • The lag time is longest if your blood sugar level is changing rapidly, after eating or if you are exercising.
  • Due to the lag time, you should to do a finger prick blood sugar check if you are considering additional insulin or hypo treatment
  • The sensor is connected to a transmitter which sends the data via wireless radio frequency to a monitoring and display device.

Blood Glucose and Interstitial Glucose Explained  

The CGM allows you to view whether your glucose is high or low, and assess how your glucose levels change while you are sleeping, after you eat when you exercise or during illness.

Some of the features of CGM are as follows;

  • Visual display of current glucose level
  • A trend arrow indicating whether glucose is falling or rising
  • A trend graph showing results over the last three, six or 24 hours
  • Alarms option to alert user to high or low levels
  • Option to download data for review

Below is some more information about the key CGM Systems Manufacturers

What is the difference between CGM and Flash Glucose Monitoring?

CGM monitors your blood sugar level continuously and sends data to your display device (a hand-held monitor or pump). So, you can set alerts for high, low or rate of change. With monitoring, it’s only when you scan your sensor that you get your reading and trends.   

Advantages of using a CGM

  • You can track your blood sugar levels all through the day and night.
  • You can see what your levels are like at times when you don’t normally test, eg during the night.
  • You can see trends: when your blood sugar levels are starting to rise or drop, so you can take action earlier.
  • Less finger prick checks.
  • Help you achieve and maintain HbA1c level to your target
  • It can help reduce hypos as you can see a downward trend before you actually go hypo.
  • You can set it to alarm at high and low levels.

Disadvantages of using a CGM 

  • You may get overwhelmed with data.
  • You still need to do some finger prick checks.
  • You may find wearing the sensor uncomfortable or unattractive.
  • You need to be motivated to benefit from the data provided

How can I get a CGM?

It depends on whether you want to use CGM for a short period (6 - 7 days) or long term (24/7). If you want to wear one for a week or two to help you look at your blood sugar trends, your clinic might be able to loan you one for that length of time. Then you can look at the data with your doctor or nurse and decide on whether you need to make any changes to how you look after your diabetes.

If you want long term CGM, it will need to be funded it in some way. You can sometimes get CGM on the NHS, but it’s not available for everyone. There are strict criteria set out by NICE around who is eligible, and you need to meet this criteria in order to get funding for a CGM.

NICE Guidance

Can I buy a CGM for myself?

Yes, but depending on which CGM you choose prices can vary.  CGM is very expensive, However, you are likely to get most benefit from the system if you get support in using it, so ask what support the company and your diabetes team can give you.

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