Performance of the Medtronic Guardian Connect vs the Free Style Libre Flash Monitor in extreme sports conditions in subjects with diabetes

In subjects with diabetes, adequate to good metabolic control is necessary for
a variety of reasons. In active subjects who perform exercising and sports
activities, adequate glucose control, including prevention of hypo- and
hyperglycemias, would allow good performance. This will even more so the case
when the sports activity is going to the strenuous and extreme.
One variation on earlier CGMs is the Guardian Connect CGM (GCCGM), with an
improved easiness of use and practical applicability under a large range of
circumstances.

Relying on a CGM device implicates the assumption, that the device will be
accurate and reliable. Recently, another device registering glucose
continuously, has entered the market: the FreeStyle Libre Flash Monitor (FLFM).

For assessment of the accuracy and reliability of both the GCCGM and the FLFM
under strenuous to extreme sports conditions, it is proposed to perform a
head-to-head comparison of these devices during the Bas van de Goor Foundation
*we bike to change diabetes* challenge in September 2017, when a combined team
of subjects with diabetes from the Netherlands and Spain will mountainbike in
the Mount Blanc massif for six days, with a total minimum distance of 218 km
and a variable amount of altitude meters (up to 7848 meters)
(https://bvdgf.org/evenementen/evenement/22613/webike2changediabetes/).

In an earlier validation study, we had to conclude, that the FLFM shows less
(albeit still acceptable) accuracy than other glucose measurement techniques.
With a standard meal test, glucose levels lagged behind with the FLFM, whereas
the results obtained with the Medtronic iPro2 Professional CGM were comparable
to those obtained with Statstrip as a *semigolden* standard (traced and aligned
to the highest level order of methodology: isotope dilution gas chromatography,
mass spectrometry).
Moreover, the FLFM tended to show lower glucose levels than actually present in
the lower regions, especially with glucose levels < 4 mmol/l (MARD approx.
20%), and higher than present glucose levels in the higher regions.
Still, user satisfaction was considerable. Despite the lack of alarms or
automated registering, the FLFM is much appreciated by many of the users.
As far as we are aware, the effect of strenuous or extreme exercise on the
performance and accuracy of both the GCCGM and the FLFM has not been studied
extensively outside a clinical setting.

The MARD of 20% of the FLFM elicits concern. Hypoglycemia risk is a major issue
during strenuous and extreme exercise. Users of glucose measurement devices
need those devices to be as accurate as possible. In our opinion, falsely low
glucose levels as shown by the FLFM in earlier research would be a disadvantage
for an exercising person with diabetes for a variety of reasons.

Primary objective To assess accuracy of GCCGM vs FLFM in 18
subjects with diabetes during a 6 day mountainbike tour in the Alps
Secondary objectives To assess the (differences in ) time in hypo-, normo- ,and
hyperglycemia (expressed in minutes per day and episodes per day). MAD and MARD
in glucose concentrations, using the same incremental glucose concentration
steps as in the validation study.

Prospective observational study with within subjects comparison of three
methods for glucose assessment: preformance characteristics of Guardian Connect
CGM, Free Style Libre Flash Monitor, and capillary measurements during
strenuous to extreme sport / exercise

Daily read-out before and during the challenge, concentrating on available
information from GCCGM and FLFM, as well as the capillary blood glucose
measurements (to be performed as standard 7 times daily, and on indication
(hypoglycemic symptoms; hypoglycemia shown on one or both of the devices, also
when no hypoglycemia symptoms are present)

in principle, CGM is a common use in subjects with diabetes performing
strenuous to extreme sports / exercise. The extra burden is wearing not one,
but two devices. No extra risks involved.