Ambulatory glucose monitoring

12 January 2017

Q. Are there options available for ambulatory glucose monitoring in primary care?

A. In my GPIT role, I'm fortunate enough to have some pre-views of coming technologies, however for this article I'm reporting as a patient's family member. My wife has insulin-dependent diabetes. To achieve good control, regular blood monitoring using finger-pricks have been required. This may need to be done several times each day, and is at best a nuisance, at worst a source of pain. An American Diabetes Association survey found that 21% of adults with type 1 diabetes never checked their blood glucose!

Ambulatory glucose monitoring (AGM) was introduced in 1999 and was seen as an improvement on self-monitoring, however it has only recently become an option beyond the trial setting. In 2013, Abbott produced its Flash Glucose Monitoring (FGM) system FreeStyle Libre, and it has been available in Ireland since November 1, 2016. We were fortunate enough to acquire the system pre-launch.

So, firstly to discuss the technology, which comprises a disposable sensor and a reader about the size of a mobile phone. The FreeStyle Libre sensor is a water resistant, adherent plastic skin patch the size of a two euro coin, including a very tiny filament (5mm in length, about the thickness of a hair) which inserts into the skin and measures glucose levels in the interstitial fluid (ISF). ISF readings are estimated to lag behind blood glucose levels by five to 10 minutes; however an in-built algorithm reduces this 'lag' period. The sensor remains in place and operational for 14 days and does not require finger-prick calibrations. After putting it on the upper arm and waiting one hour, it begins reading glucose and trend information, which it stores for eight hours.

The second half of the kit is the compact, handheld reader that displays glucose readings and stores up to 90 days of glucose data. It also doubles as a traditional glucometer. To use the reader, it is held for one second up to 4cm above the sensor (it can be used through clothes) and a flash glucose reading is obtained, for which Abbott claims greater than 99% accuracy. Some clever analyses are instantly available on the reader screen; however more detail is available by downloading the easy to use software from the Freestyle website.

So what of the personal user experience? We had read blogs from users in the UK who have had Libre for longer, and the reviews were mixed, so our initial anxiety was about accuracy. Therefore, understandably in the first few days there was a lot of checking with finger pricks. Our statistically insignificant opinion based on one patient is that it's very accurate! We have also found it easy to use, convenient and indeed quite liberating because of the ability to scan in the shop, the restaurant, the car or while exercising. Rather than the painful ceremony of the finger prick, the reader can be pulled out of pocket or bag, flashed across the clothed arm and an instant reading is obtained. This has led to more testing and probably better insight into the competing effects of insulin, exercise and different foods. Indeed, the system software has a professional section that includes an insulin calculator, but we haven't ventured there yet! The other reports on the reader or PC software (connect via micro USB) are very informative.

Each sensor has an applicator for attaching it to the arm. The application is not dissimilar to using a name stamp, and it sticks to the arm first time. The procedure is pain-less. We have been relatively cautious about water, but it is claimed to be sweat and waterproof, and the blogs seem to back this up. The sensor turns itself off after 14 days, the removal is straightforward, and you replace on a different site on the arm.

There have been previous continuous glucose monitors, and there will probably be similar in the future, but this appears to be a significant step forward. The main practical problem is that the cost of the Libre is covered neither by General Medi-cal Service (GMS) or Long Term Illness (LTI) schemes. The sensors are expensive at E60 each every two weeks, however test strips are not cheap either and the costs are comparable if you test your blood a few times every day. So this is not for everyone, but I would definitely consider it for any insulin-dependent patient with diabetes requiring regular monitoring.

More information is available at www.freestylelibre.co.uk

Declaration of Interest: Abbott Pharmaceuticals have no influence or control over the author, however our first sensor and reader were provided free of charge.

Dr Conor O'Shea, GPIT national co-ordinator