What is Continuous Glucose Monitoring? (CGM)

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What is Continuous Glucose Monitoring? (CGM)

Continuous glucose monitoring (CGM) allows you to track your blood glucose (sugar) levels any time, day and night. This wearable technology has a tiny sensor that sits under the skin and automatically transmits blood sugar readings, data and alerts to a reader or smartphone so that you can make better decisions about managing your diabetes.

How Does CGM Work?

Continuous glucose monitoring refers to the activity of constantly measuring blood sugar levels 24-hours a day – either in real-time or retrospectively. This is achieved with the help of wearable technology called a continuous glucose monitor (CGM).

A CGM is made up of three parts:

  • A small sensor sits just under the skin which measures your blood sugar levels.
  • A transmitter is attached to the sensor and sends the readings to the display device.
  • A display device shows the results – this can be a separate hand-held device or your mobile phone.

Sensors can typically be worn for 7-14 days before they need to be replaced. They are generally waterproof and attached to the skin with adhesive patches. The sensor should be calibrated twice daily by checking your CGM levels against your finger-prick glucose levels.

Different CGM devices have different special features. Some systems can be integrated with insulin pumps. Most CGMs can be programmed to send alerts when glucose levels go too high or too low. Some models can automatically send data or alarms to a second person’s smartphone. This is especially helpful for parents or caregivers monitoring a child’s condition overnight.

How is CGM Different from a Finger-Prick Test?

A CGM works by measuring the amount of glucose in your interstitial fluid – the fluid between your cells. Testing your blood sugar with a traditional blood glucose meter is an accurate snapshot of your blood sugar level at that point in time, but the blood glucose reading from your interstitial fluid has a slight delay. CGM gives you a bigger picture of your blood sugar levels: where they’ve been, where they are now and where they are headed.

Most CGM users can reduce the number of times they finger-prick per day, but you’ll still need to do some finger-prick testing when calibrating your CGM. Because there is a slight delay in your CGM blood glucose readings, you should do a finger-prick test if you’re thinking of changing your treatment to get the most accurate results.

What are the Benefits of Continuous Glucose Monitors?

There are several key advantages to using a CGM device:

  • Gain a better picture of your glucose levels every day – By tracking your blood sugar levels 24-hours a day, you get a more complete picture of your blood sugar levels.
  • Avoid dangerous hypos – As soon as you see your blood sugar start to drop, you can take action to avoid dangerous hypos.
  • Improve your HbA1c levels – Using the data from your CGM to tailor your insulin plan, you might see an improvement in your HbA1c levels over time.
  • Receive automated alerts when your levels go too high or low – Set alarms to take quick action to maintain your blood sugar targets.
  • Share data – Get extra security by sharing data with a family member who can set up alerts if your levels go too low or too high. Easily share information with your health team and see patterns in your blood sugar trends.
  • Reduce the number of times you’ll need to finger-prick – Although they can’t be eliminated completely, you can generally reduce the number of times you’ll need to do a finger-prick test.


When used effectively, a CGM can help you better manage your blood sugar levels. Proper glucose management means fewer diabetic complications and better long-term health.

Another key advantage of continuous glucose monitoring is the psychological benefit of feeling more in control of your health. Many people living with diabetes suffer from mental health issues such as depression and anxiety about sudden hypos. By using a continuous glucose monitoring device, you might experience greater peace of mind knowing that a sudden swing in blood glucose levels will not go unnoticed.

How Can I get a CGM?

The first thing to do is speak to your diabetes care team. They can help you assess if a CGM is right for you.

If you’re struggling with your blood sugar levels, you can request a continuous glucose monitor from your clinic for a short-term loan. This will allow you to assess the patterns in your glucose levels and make treatment adjustments to meet your blood sugar targets as necessary. However, you might have to wait if the device is already on loan.


Eligibility for CGM on the NHS

Funding criteria for receiving CGM on the NHS are set by the National Institute for Health and Care Excellence (NICE). Unfortunately, the most recent NICE guidelines recommend against routinely offering CGM to all type 1 diabetics. For this reason, many patients choose to self-fund their CGM devices.

To receive funding for a CGM, you must meet the strict criteria set out by NICE. In all cases of NHS-funded CGM devices, you should be prepared to show that you are using your CGM 70% of the time and reviewing the data and trends with your healthcare team.


Self-funding your CGM

If you are not eligible for an NHS-funded CGM, you can privately purchase your chosen CGM solution.

Estimated prices vary greatly but you should expect that a standalone CGM (one that is not part of an integrated insulin pump solution) costs approximately £1,000. Monitors that work with an insulin pump cost approximately £500. Sensors are priced from £40 to £60.

Whether your CGM is funded by the NHS or privately, you should make sure that you have arranged support for continuous glucose monitoring before procuring your device. For CGM to be truly effective, you’ll need expert knowledge on which strategies to use to reduce hypos and improve your HbA1c level.

What does a CGM Device Look Like?

There are two types of CGM solutions: real-time and intermittently scanned. Real-time CGMs measure your blood glucose roughly every five minutes. Flash glucose monitoring is a type of intermittently scanned CGM that requires you to manually scan the sensor to get your blood glucose data.

The sensor is typically small and discreet – approximately the size of a £2 coin. The transmitter is attached to the sensor. Depending on the CGM, the transmitter can either be reused or must be replaced. The sensor is attached to the skin, usually on the back of the arm or the belly.

The receiver varies in appearance and functionality depending on the type of CGM. Some CGMs have small hand-held receivers with screens that can be worn in your pocket or a small pouch on your body. Other people choose to transmit their data directly to their mobile phone and access it via an app.

If your CGM device is a part of an integrated solution, the data receiver and display will be located on the insulin pump.

Are there Alternatives to CGM?

Although continuous glucose monitoring can be helpful if you use insulin and would like to understand your blood sugar levels better, it’s not the only option. Continuous glucose monitors can be complicated to understand and use, which means they might not be the right solution for everyone.

You can regularly check your blood sugar by doing a finger-prick test and using a blood glucose meter. There are many different types of blood glucose meters on the market with different features to suit your specific needs. When choosing a blood sugar monitor, you should be sure to check with your healthcare provider to make sure that you choose a model that has the right features for you. Test strips should be provided on prescription, but you should check that your GP can provide strips that are compatible with your meter.

Is CGM Right for Me?

CGM systems have been shown to help people with diabetes keep their blood sugar levels stable, reducing episodes of both hypos and hypers and decreasing the risk of complications from diabetes. However, continuous glucose monitoring isn’t a cure-all. To get the most out of continuous glucose monitoring, you’ll need to work carefully with your support team to analyse your results and discuss the best strategies for your diabetes care.


Get in touch with us today to discuss if CGM is right for you.

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Carol Willis

Carol Willis - Diabetes Clinic Facilitator

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