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The standard-of-care for measuring glucose levels and determine whether insulin is needed is by “finger-stick” blood glucose meters. A drop of blood, usually drawn by piercing the skin of a finger, is brought in contact with a test strip. A chemical reaction triggers an electrochemical sensor or a colour reaction that is detected in a reader. The drawback of this method is that only a few measurements can be performed in the course of a day.
Tighter glycaemic control
The development of a control system that infuses insulin on the basis of glucose measurements could permit tighter glycaemic control and improve clinical outcome without increasing workload of the health care professionals (Plank2006).
Only a few commercially available sensors that allow continuously monitoring the blood glucose level (CGM) have been approved for the market. These sensors rely on electrochemical detection of an enzymatic reaction and are minimally invasive. Two non-invasive systems, GlucoWatch and Pendra, have reached approval by the US Food and Drug Administration (FDA) or achieved a CE marking. The first relies on iontophoresis for sample collection and electrochemical sensing while the other employs impedance spectroscopy for glucose measurement. However, the availability of both systems has ceased due to financial difficulties of their manufacturers.
Other sensor technologies are currently being tested for their suitability for glucose monitoring. The most promising technologies can broadly be classified as follows:
Moreover, alternatives for invasive sampling are being investigated for electrochemical detection, for example samples may also be collected by iontophoresis or suction blister extraction trough the skin. Despite significant efforts these technologies are still in a development or evaluation phase and yet have to prove their reliability and accuracy.
The REACTION project will develop continuous glucose monitoring device in closed loop operation and to develop and integrate prototypes of two different, non-invasive and minimally invasive principles based on 1) impedance spectroscopy and 2) Infrared spectroscopy
Current CGMs not sufficiently accurate
Requirements for in vitro glucose monitoring systems for self-testing by laypersons that measure glucose concentrations in capillary blood samples are specified in the ISO norm ISO 15197:2003.
According to Klonoff (Klonoff2005), currently available CGMs that provide real-time readings are not sufficiently accurate to allow making therapeutic decisions such as whether to dose insulin or eat. No current glucose monitoring system achieves relative accuracy better than 15% across the normal range. The problem of accuracy takes several forms and cannot be addressed with a simple answer. It depends on the application.
Moreover, the measurement of glucose performed in vivo is unpredictably influenced by various substances of the body fluids such as proteins, cholesterol and so on. Accordingly, the newly published guidelines by CLSI (Performance Metrics for Continuous Interstitial Glucose Monitoring (POCT05-A)) does not give a definite number of accuracy needed for safe and effective use of CGM. This text reflects the state-of-the-art knowledge in CGM systems, in particular relating to Automatic Glucose Control (AGC), and serves as guideline for developers as well as regulatory bodies such as the FDA for evaluating such systems. For this reason we do not attempt to set an a priori target for the accuracy to be obtained by the developed and investigated glucose sensors. Rather we set as our goal to evaluate the performance data of the investigated systems against this background and to meet or exceed the state-of-the-art.
The objective of the clinical trials in REACTION is to study the precise need for measurement accuracy for CGM. Based on these studies as well as on the approved guidelines (POCT05-A) the developed sensors will be evaluated for their applicability for safe use in Automatic Glucose Control systems
ePatch sensor technology
The need for a new wireless sensor technology for monitoring physiologic parameters and be wearable by patients at home has been discussed for a long time, but emerged strongly in the literature since 2005. The first ePatches were developed by DELTA from 2006 to 2008 based on off-the-shelf-components in a reusable sensor unit based PCB board (Haar2008).
In further developments, sEMG (surface Electric Myografic) sensors have been integrated in ePatches, and proof of principle has been made on reflective pulse oximetry sensors designed to be integrated in ePatches. In another study, 10 patients wore ePatches for 5x24 hours while the ePatches sent ECG-data from the patients’ home to the EPR via a mobile phone (Nielsen2008).
The ePatch technology will be taken further in the REACTION project. ePatch Continuous Glucose Monitoring sensors based on Impedance Spectroscopy and IR spectroscopy will be developed and tested in field trials. Other sensors for skin temperature and pulse oximetry will be manufactured
A new ePatch prototype suitable for mass manufacturing and disposable technology will be developed and tested