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By Michele D. Huie
TCOYD Newsletter, Vol. 27, 2008
Almost one year ago,
the FDA approved
Abbott's FreeStyle
Navigator continuous
glucose monitoring
(“CGM”) system. There are
now three CGM devices
available in the U.S. by
prescription: MiniMed’s
Paradigm Real-Time
system, Dexcom Seven,
and Abbott Navigator.
Thankfully, more
and more insurance
companies are admitting
to the reality of this lifesaving,
life-prolonging,
and complication-deterring
tool; see related article .
What’s CGM Again?
To review, CGM is technology that
continuously measures the glucose level
in the body’s interstitial fluid that floats
around between our cells. It does this
through a small sensor that the user
places under the skin. The interstitial
fluid glucose value is interpreted and
calculated into a blood sugar value—in
the units we are accustomed to—mg/dl
or mmol. The blood sugar numbers are
transmitted to a receiver, a hand held
device, about the size of a cell phone.
 What Are the Advantages?
CGM makes us a little less metabolically
handicapped. It enables us to see
the variability in our blood sugars, and
actively maintain steadier, healthier
glucose levels—spending a little less
time REACTING to when we are out
of range. Testing your blood sugar six
times a day gives you six data points;
CGM provides a steady stream of information—
including blood sugar trends,
unexpected patterns, and essential
warnings for out of range glucose.
The Device
The Navigator comes with a disposable
insertion device for the sensor.
When the 6 mm sensor is inserted,
a plastic shell remains into which
the transmitter is snapped. The total
footprint is about 2” by 1 ¼”. The
glucose values are read on a monitor
(3” x 2.5”) that doubles as a Freestyle
Flash blood glucose meter. I like this
feature, as it means one less thing to
carry around.
Calibration
The Navigator has a 10-hour wait
period when you first put in a new
sensor while the body and the sensor
get used to talking to each other. At
the end of that period, the Navigator
requests a “calibration” finger stick—
taking a blood sugar using the meter
built into the monitor—after which
continuous sensing commences.
All CGM devices require a start up
calibration and all need recalibrations
at intervals; however, it seems that
over the 5 day (indicated) life of the
Navigator sensor, there was far less
calibrating necessary than with other
devices. Another noticeable difference
for me was the intelligent design that
rejects calibrations taken when the
blood sugar is rapidly rising or falling.
Using the Navigator
The Navigator’s wireless range is
officially 10 feet, but I have left the
monitor in a colleague’s office down
the hall, and returning an hour later,
found an uninterrupted string of glucose values.The Navigator displays
the blood sugar in big numbers on the
screen, and provides updated glucose
values every minute. It also displays an
arrow—either straight across, indicating
a steady blood sugar; an arrow at a 45
degree angle, indicating blood sugars
changing at a rate of 60 mg/dl per hour;
or an arrow pointing straight up or
down meaning the blood sugar is rising
or falling at a rate faster than 120 mg/dl.
Advance Warning of
Highs and Lows
Ten to 30 minutes in advance of
going outside the range the user sets
for for high/low alarms, the Navigator
will predict and warn the user of the
potential problem ahead. The first
few times this happened, I found the
beeping irritating (I was within range,
and felt fine) until I unexpectedly
crashed, or shot up like a rocket. The
Navigator is, in some ways, smarter
than I am. This is a great feature.
For more information on the Navigator visit
www.freestylenavigator.com ,
read the diabetes bloggers, or visit
www.childrenwithdiabetes.com for a
side-by-side feature/spec comparison.
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