Whilst spending the afternoon deep water soloing in Devon last month I spotted this on the upper arm of a nearby climber. What was it? I hadn't a clue! Later that evening David Hillebrandt, honorary medical advisor to the BMC, joined us for dinner and knew the answer straight away - a Continuous Glucose Monitor (CGM).
A CGM takes a glucose measurement from the interstitial fluid* found immediately below the skin and transmits the result to a nearby receiver. Devices vary. "Continuous" monitors take measurements at set intervals, whilst "flash" devices only take a recording after a request has been made. "Continuous" CGM's have two distinct advantages. First, they can be connected to an alarm and alert patients if measurements fall outside a predetermined range. Second, they have the potential to "talk" to a nearby pump worn on the skin and administer a dose of insulin. Amazingly, this "artificial pancreas" system may eventually lead to a time when insulin dependent diabetics will no longer need to take blood glucose measurements or inject insulin!
Typically, CGM devices are replaced after one or two weeks. However implants are now available which can stay in place for several months. Naturally this all comes at a price and CGM's are not yet widely available, however it is clear that the management of patients with diabetes is going through a radical transformation. Old mountain medics like me need to keep up with the times!
We asked Paul Richards, a GP and Diploma in Mountain Medicine faculty member, to tell us about his experience with a CGM.
Abbott Freestyle Libre stores the last eight hours of interstitial glucose measurements and transmits them either to a reader (see photograph) or via an app onto a mobile phone or computer. The device is worn for 14 days. Finger prick calibration is not required.
Initially I was diagnosed with Type II Diabetes Mellitus (DM2) in 2002 despite being fit and slim at the time. By 2006 I was on insulin with a revised diagnosis of Latent Autoimmune Diabetes of Adults (LADA) or "Slow Burning Insulitis"**. It is important for young medics to realise that not all "middle aged" diabetics are DM2 and those who rapidly progress to needing insulin should be re-evaluated as having LADA.
What made you start using a CGM?
Desire to improve DM control. I particularly needed information regarding night blood glucose trends whilst asleep. Also, much easier to monitor blood sugars whilst on mountains or during activities especially in inclement weather. This is easy via a mobile phone and it's near field communication (NFC) reader as it just needs to be held against the sensor on the arm and even works through a fleece and waterproof jacket.
What difference has it made to you and your diabetes?
Confirmation of no nocturnal hypoglycaemia events.
Improvement of glucose "time in target range" by 54%.
Have you encountered any problems with using it?
The delay between interstitial fluid glucose, finger capillary glucose and cerebral glucose must be considered so if the Freestyl Libre indicates a low and falling glucose or there are symptoms of possibly hypoglycaemia, a capillary blood glucose must still be taken. Thus this device does not completely replace a usual blood glucometer which must also be carried.
The mobile phone app isn't as sophisticated as the dedicated Libre meter. With the latter, insulin doses, events such as exercise etc can be recorded and uploaded to online platforms such as Diasend for transmission to diabetic specialist or clinic. This facility is also possible from the phone app but only for glucose readings, the other data is not transmitted. The app requires further development.
Such has been the demand for freestyle Libre that there are supply delays and Abbott, the manufacturer are limiting delivery to existing customers only at 2 per month.
Although NICE recommended use and NHS availability in November 2017, the clause 'subject to local policy' has meant that many CCG's (the primary care commissioning groups) are not as yet funding their NHS use due to budgetary restraints. Thus, for many they are only available for private purchase. VAT is deducted if a declaration of personal use by a diabetic is made on the order form giving a price of £48.29 each inclusive of UK delivery.
Do you see a time where you'll move towards a CGM that could see you never having to measure your own glucose or administer insulin ever again?
Very much so. This is the way forwards. A CGM which alerts automatically when there is a downward glucose trajectory with risk of hypoglycaemia would be very useful. A 'Closed System' or 'artificial pancreas' where a CGM monitors glucose and AI software calculates the appropriate insulin dose which is then automatically given by pump would be incredibly liberating. Various systems are in development but not yet a reliable reality for most diabetics.
Quincy, a male Koala at San Diego Zoo, has his diabetes monitored by a CGM.
*The interstitial measurement lags several minutes behind the glucose concentration found in the blood.
**Patients with LADA produce autoantibodies that destroy pancreatic islet cells and halt the production of insulin. Those with DM 2 still produce insulin, however muscle, adipose tissue and liver cells are unable to absorb glucose. DM 2 is commonly associated with obesity.