Page 144 - Glucose Monitoring Devices

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Available CGM systems

creating significant inaccuracies when comparing data between trials. Sensor lag
describes the delay in glucose diffusion across the capillary bed, into the interstitial
space, and finally being registered by the CGM sensor. Technological advances
have seen sensor lag reduce to a few minutes from the 15 min reported in early
CGM systems. Nonetheless, the cumulative effect of this delay can result in sensor
measurements drifting further away from corresponding capillary blood glucose
values. Systems susceptible to sensor drift are required to undergo twice-daily
CGM calibration during glycemic steady states to overcome the significant inaccu-
racy resulting from sensor drift. Significant improvements in CGMs accuracy has
seen the UK Driver and Vehicle Licensing Agency update their guidelines to
permit its use among car and motorcycle drivers on insulin therapy. However,
individuals are obligated to measure their capillary glucose if they experience
symptoms of hypoglycaemia or blood glucose levels are 4mmol/L or below. Alarm
fatigue is well described in CGM where hypo- and hyperglycemia alarm notifica-
tions are intrinsic components in establishing clinical efficacy and in extreme cases
cannot be disabled. Shivers et al. addressed the artificially higher thresholds set for
low glucose alarms to increase detection sensitivity, however inversely reducing
specificity and subjecting users to more false-positive alarms [67]. This, in turn,
increases alarm fatigue, drives users to ignore alarms, and ultimately abandon
CGM [67]. The signal loss to receiver/smartphone and false measurements due
to physical sensor compression are additional hardware issues with significant
implications when responsible for automated insulin delivery within a closed-
loop AP system. Lastly, unless financially reimbursed by healthcare providers, per-
manent use of CGM is an expensive venture and economically out of reach for
most individuals.

Available CGM systems
Positive clinical trial outcomes have contributed to a rise in the popularity and num-
ber of available CGM systems. Listed below are a summary of randomised
controlled CGM trials and the currently available CGM systems in the United
Kingdom (Tables 7.1 and 7.2).

Dexcom
The Dexcom G6 is a standalone CGM system with superior accuracy (MARD 9%)
compared to its competitors. The sensor iseasilyinsertedand requires a2hwarm-
up period before glucose levels are uploaded for user access. Once active, glucose
measurements are transmitted via Bluetooth to either a proprietary Dexcom
receiver, the Dexcom smartphone application, or a sensor-augmented insulin
pump (e.g., Tandem T-slim). The G6 comes equipped with a simple to use
one-touch sensor applicator, boasts an extended sensor life span of 10 days, and
is not affected by acetaminophen. Of greatest significance to users is the