Therapeutics update: Continuous glucose monitoring

Dr Shammy Noor explains the advantages and reliability of continuous blood glucose monitoring

Traditional blood glucose testing
Fingerstick blood testing has been used for generations. It can be convenient, accessible and provides immediate results. Downsides include:

Limited information. Fingerstick testing provides a snapshot of blood glucose levels, which fluctuate throughout the day, influenced by stress, exercise and medication. A snapshot does not give a direction of travel. A blood glucose (BG) of 5 that is rapidly dropping needs a different response to a BG of 5 that is stable over time, but a fingerstick can’t tell the difference.
Discomfort and inconvenience. Frequent finger pricks are painful. If calluses or scar tissue form, the accuracy of the reading drops.
Cost. The cost of test strips and lancets adds up.
If they are used more than six times per day, they become less cost effective than continuous glucose monitoring (CGM).
User error. Not washing hands before testing, not using enough blood and not properly calibrating the meter can lead to incorrect readings.

How CGMs work
A small sensor is inserted under the skin, usually on the abdomen or arm. The sensor measures glucose levels in the interstitial fluid rather than capillary glucose that a fingerstick measures.

The sensor measures the levels every few minutes and transmits this information to a device such as a smartphone or monitor.

Flash glucose monitoring is slightly different in that it doesn’t transmit a live reading. Instead, the user scans the device, which gives a current update and the saved readings on the sensor. Flash glucose monitoring is technically not CGM.

Advantages

Real-time tracking and trends. CGM provides real-time glucose level data and tells the user if glucose is going up or down, allowing them to make more informed decisions about food, exercise and medication.
Alerts and notifications. CGM can send alerts when glucose levels are too high or too low, enabling early intervention.
More information for the doctor. The data can be read by a clinic to help monitor the patient.
No more bleeding fingers and kits to carry around. This is life-changing for people who are living with diabetes.
Many patients don’t test often enough with fingersticks, but CGM testing requires no extra effort and the test is guaranteed to be done throughout the day.

Problems

Cost. The technology can be more expensive.
Skin irritation or allergic reactions to the adhesive are possible.
Delayed readings. CGMs provide interstitial glucose readings, which lag behind blood glucose by around 15 minutes. If glucose levels are changing rapidly, the readings may not be accurate. It is important that the patient knows this, to avoid making an incorrect insulin dosing decision.

What devices are available?
Abbott offers the FreeStyle Libre system, which uses a small sensor placed on the back of the upper arm and can be worn for up to 14 days.

The system provides glucose readings by scanning the sensor with a handheld reader or smartphone app. The first Libre was a flash glucose monitoring device but the more recent Libre 2 and Libre 3 are full CGM devices.

Dexcom offers several CGM devices, including the Dexcom G6 and the Dexcom One, which is a standalone device that can be worn for up to 10 days and provides real-time glucose data via a smartphone app.

Both Abbot and Dexcom monitors can be prescribed on a standard GP prescription.

Numerous other manufacturers make sensors including Medtronic (Guardian Connect), Senseonics (Eversense and SugarBEAT). However these are not available on prescription, are not all available in the UK, and would generally be given by a hospital clinic or bought by the patient.

NICE guidelines and when to prescribe
In 2022 NICE updated its guidelines to recommend flash or CGM for all adults with type 1 diabetes.

These new guidelines represent a shift towards a better understanding of technology as an integral part of diabetes management, rather than a technological luxury.

NICE NG17 (Type 1 diabetes in adults: diagnosis and management) now states: ‘Offer adults with type 1 diabetes a choice of real-time monitoring (rtCGM) or intermittently scanned monitoring (isCGM, commonly referred to as ‘flash’), based on their individual preferences, needs, characteristics, and the functionality of the devices available.’

For type 2 diabetes, NICE also recommends CGM, but only for adults on multiple daily insulin injections and with any of the following:

Recurrent or severe hypoglycaemia.
Impaired hypoglycaemia awareness.
Disability that means they cannot self-monitor.
The need to self-measure at least eight times a day.

How to prescribe and educate
For Libre and Dexcom One, issue a prescription in the same way you would for glucose testing strips. CGM is usually initiated in secondary care but GPs with sufficient expertise can initiate monitoring if local guidelines allow.

Remember the patient will need a smartphone to receive the data. Most modern phones will be compatible. They will need to download an app to use it.

Patients need education on use of the device.

Most patients can learn to use it in less than an hour and will find it much easier than fingersticks. Ensure patient education is appropriate and effective for everyone. Ensure patients understand the readings are delayed by 15 minutes so if they are changing fast, they should use a fingerstick test to be sure of the true reading. Leave a small quantity of testing strips on the repeat prescription.

To offer education on use of the device, you could:

Familiarise yourself with how to use the device and show the patient in the consultation.
As a longstanding user I take this approach.
Ensure a practice nurse is familiar with the product and can talk the patient through the process.
Send the patient links to the manufacturer’s educational videos.

The patient also needs to be taught how to use the data from the monitoring machines, which is best done by their secondary care clinic or diabetes specialist nurse.

Audit your type 1 diabetics
Perform a practice search for patients with type 1 diabetes. If they are not on a CGM, flag this to discuss at their next diabetes review, call them in to discuss it or encourage them to raise it with their diabetes team.

A personal view on glucose monitoring – ‘I can play my guitar again’

I recently ‘celebrated’ my 20th year as a type 1 diabetic. Since this coincided with the 100th anniversary of the discovery of insulin, I spent time reflecting on the progress we have made in this field of care, and also on my own journey.

The 1923 Nobel Prize lecture by Frederick Banting talks of giving enough insulin to make the patient’s urine sugar free, but not so much to make them hypoglycaemic. A century on in 2023, the same principles apply for the management of type 1 diabetes.

In order to follow this principle, the patient needs to know their glucose levels and have the means to adjust them and deliver insulin.

There have been many life-changing advances in my diabetes care over the last 20 years. First came my insulin pump. Then there was my CGM. This was an absolute game-changer – no more sore fingers . I can finally play my guitar again.

The next innovation was my tubeless pump. I used to get my tubes caught on door handles every few days. Then I took the plunge and built a homemade closed loop ‘artificial pancreas’. This was thanks to the inspirational work of the group wearenotwaiting.org. Happily, the NHS is now pushing on to make this more available.

When managing a long-term illness is no longer a chore, people manage it better. When they manage it better, they will live happier and healthier lives. And the NHS might be a little less busy too.

Dr Shammy Noor is a GP in Lichfield, Staffordshire