Dexcom's labeling describes a sensor coated with glucose oxidase. The enzyme reacts with glucose, and the hydrogen peroxide that results is oxidized at a platinum working electrode, which produces a small current. In the terms of Unit 7, that is a first-generation, peroxide-detecting design.
It is the classic enzyme electrode, miniaturized and wrapped in membranes.
THE SIGNAL
Reading nanoamps
CurrentThe sensor's current is only nanoamps
ProportionalIn its working range, more glucose means more current
ConversionThe transmitter digitizes the current, and the algorithm scales it to mg/dL
The conversion factor is set by factory calibration.
INTERFERENCE
What can fool the sensor
AcetaminophenLabeling describes the sensor as blocking it at typical doses, using its selective layers
HydroxyureaLabeling warns this drug can falsely raise readings
The ruleAlways check the current labeling for substances that affect readings
Interference rejection is a chemistry problem solved in the layers.
WARM-UP
Time to settle
WhyAfter insertion, the tissue around the sensor and the sensor itself need time to stabilize
How longAbout 2 hours for G6, and about 30 minutes for G7
First dayEarly readings can be less accurate while the sensor settles in
A short wait after insertion makes the early signal more trustworthy.
THE ALGORITHM
Raw current in, smooth glucose out
FilteringRemoves noise from the raw signal
CompensationCorrects for temperature and sensitivity
PlausibilityLimits changes that would be physiologically impossible
TrendEstimates direction and rate of change, and can warn of a coming low
Software is as important to accuracy as chemistry.
UNIT 11 STUDY COMPLETE
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You've covered the chemistry, interference, warm-up, and algorithms behind a Dexcom reading.