Glucose monitoring: Flash (CGM) vs Finger Stick vs Non-contact
At Occuity, we're working on a non-invasive glucose meter, that we believe has the potential to improve the lives of hundreds of millions of people, by replacing invasive tests.
In this article, we thought it would be good to look at the existing methods of blood glucose monitoring and why we believe our non-invasive device could offer an excellent alternative.
A normal question for all those who have been diagnosed with diabetes to ask is "What is the best way to measure glucose levels?" - it is one for which the answer will most likely be ‘it depends.’ Just as everyone’s diabetes is personal to them, so too is the way in which they will monitor and manage their condition.
With this in mind, let’s look at two of the most commonly used monitoring options starting with the finger stick test. First developed in the 1960s, the finger stick test involves using a lancet to extract a drop of blood which can be used to measure blood glucose levels. Originally only available in health settings, the technology has evolved to the extent that portable testing kits can now be used in the home and elsewhere
This development has enabled individuals to carry out tests multiple times a day. This not only helps people to manage their condition it also opens up lifestyle choices. For example, testing before a meal could enable people to choose from a wider menu, whilst testing either before or after exercise may indicate whether food or insulin interventions are required.
The accuracy of finger-prick tests is governed by an international standard, ISO 15197.  This requires blood glucose monitor tests to have a certain level of accuracy when compared to tests carried out under laboratory conditions. That level of required accuracy was strengthened in 2013, leaving diabetes.co.uk  to comment that:
“The move to the tighter 2013 standards is a positive advance as it will mean blood glucose meters will need to be more accurate and therefore provide greater confidence to us as users of the meters.”
We’ve seen above how finger stick tests can help with the day to day management of diabetes. However, there are a few downsides to their use. Perhaps most importantly, these tests do require the extraction of blood, and that can be a painful experience. This may lead individuals to test less frequently than they should and therefore not manage their condition appropriately.
Another area of concern is that, whilst monitors are expected to have a certain level of accuracy, it has been shown that test results can be affected by a range of factors, including temperature, humidity and even food residue on fingers. We also have to factor in the cost of providing testing kits as well as the environmental costs associated with the disposal of lancets and test strips.
So could flash glucose monitoring be the answer? Flash glucose monitors consist of a small round sensor with a tiny needle that reads glucose levels just under the top layer of skin. The sensor is generally applied to the skin of the upper arm and requires replacing at least every fourteen days. 
Using a smartphone or dedicated device, glucose readings can be checked as often as required by holding the device up to the sensor. A variant, called a continuous glucose monitor (CGM), enables data to be continuously transmitted to a reader via Bluetooth.
Whilst the application of the sensor is said to be "generally painless" and needs to be done far less frequently than the finger stick tests - a distinct bonus when compared to finger-prick testing is that unfortunately, CGM's are not suitable for every skin type and the patches have been known to cause irritation for some people. There is also a small risk that the sensor can be knocked or damaged. However, with the sensor permanently in place, readings can not only be taken as required but they can also be sent to clinicians or carers, enabling those who may need a little extra help in monitoring their condition to receive improved levels of care.
Being able to monitor glucose levels on an ad-hoc basis can help in improving the management of diabetes. One 2021 study  concluded that:
“patients who use flash glucose monitoring might expect to achieve significant improvement in HbA1c and glycemic parameters and several associated benefits.”
However, another study  cautioned that because the sensor takes information from just under the skin rather than from blood, there can be a time lag in delivering accurate data, and there may therefore be times when finger stick tests will still need to be used.
The benefits shown above prompted the NHS to include in its long term plan the ambition that:
“in line with clinical guidelines, patients with Type 1 diabetes benefit from life-changing flash glucose monitors from April 2019.” 
It has to be said that flash glucose monitors are more expensive than finger-prick tests, and they are not suitable for everyone. More care needs to be taken when dressing and undressing in order to avoid dislodging the sensor. In addition, some individuals may feel uncomfortable about visibly wearing the sensor when in public.
So is there another alternative, one which is non-invasive and cost-effective and which delivers accurate readings on demand? Well, glucose levels show up in many different ways, and numerous studies have shown that there is a direct correlation between fluctuations in blood glucose and changes in the anterior chamber of the eye.
Building on its existing expertise, Occuity is in the research and development phase of a cost-effective handheld optical device, about the size of a pen, which can be used to read those changes. Simply by holding the device in front of an eye for a few seconds, glucose levels could be measured and read, either directly or by transfer to a phone. The device is still under development and we have got a way to go, but we believe that this could deliver the benefit of flash monitoring without the disadvantages of a wearable device.
This blog is not intended as advice or guidance. For expert advice, always speak to your healthcare professional