How the Glucose Sensor Works
Continuous Glucose Monitoring
Objective
• To learn the components of the Glucose Sensor and how
the Glucose Sensor works in interstitial fluid
Key Points
• Proper technique when handling and inserting the Glucose
Sensor as well as ongoing care leads to a successful CGM
experience
• The Glucose Sensor requires calibration with a blood
glucose meter
Glucose Sensor Components
Introducer
Needle Handle
Introducer
Needle
Sensor Electrode
inside the needle
Connector to
MiniLink or iPro
Body
Glucose Sensor Components
Connector
Introducer
Needle Handle
Attaches to the
MiniLink
Transmitter or
iPro Recorder
Never hold or pick
the Sensor up by
the needle handle
Introducer
Needle
– 22 gauge (1/2
diameter)
– Bevel faces down
– Discard after
insertion
Sensor Electrode
inside the needle
Body
Pick up the
Sensor on either
side of the
Connector
The Sensor Electrode Sits Inside the Introducer
Needle
Reference electrode
Closest to the skin
Working electrode
Counter electrode
Maintaining an Optimal Sensor Placement Ensures Success
Layers of the Glucose Sensor
Semi Permeable Membrane
Membrane
Selective to glucose and oxygen
Enzyme
Enzyme
The membrane surrounds a
glucose oxydase enzyme
Electrode
Electrode
Outermost Layer of the Glucose Sensor
Semi Permeable Membrane
Selective to glucose and oxygen
• Ensures biocompatibility
• Maintains the required glucose to
oxygen ratio required for diffusion to
the enzyme layer
• Functions as a glucose limiting
membrane
Membrane
Enzyme
Electrode
The Glucose Sensor Consists of 3 Layers
Semi Permeable Membrane
Selective to glucose and oxygen
Enzyme
The membrane surrounds a
glucose oxydase enzyme
Electrode
1
Glucose and Oxygen Enter Membrane
A semi permeable membrane that is
very selective to glucose and oxygen
Membrane
The Membrane is required for
biocompatibility
Enzyme
In subcutaneous tissue
Glucose = 72 to 360 mg/dl
Oxygen = 0.9 mg/dl
Glucose is 5 times more prevalent in
subcutaneous tissue
Electrode
1
Glucose and Oxygen Enter Membrane
• When the glucose and
oxygen come in
contact with the
glucose oxidase
enzyme, the first
chemical reaction
takes place
Glucose
and
Oxygen
Membrane
Enzyme
Electrode
2
First Chemical Reaction
• Glucose and oxygen
come in contact with
the glucose oxidase
enzyme
• Glucose and oxygen
are converted into
Hydrogen Peroxide
(H2O2) and gluconic
acid
Glucose
and
Oxygen
Membrane
Enzyme
Electrode
Gly
H
2O2
Acid
3
Second Chemical Reaction
• H2O2 seeps through to
the Electrode layer
• A voltage is applied to
the Electrode, causing
H2O2
to breakdown into:
 Hydrogen
 Oxygen
 2 electrons
Membrane
Enzyme
Electrode
H2O2
2e-
The more glucose in your body, the more H2O2 generated.
The more H2O2, the more current generated.
Converting ISIG to a Glucose Sensor Value
• The 2 electrons
generate a current
called ISIG
• ISIG is converted to a
sensor glucose value
when a BG meter value
is entered into the pump
or monitor for
calibration
Membrane
Enzyme
Electrode
The ISIG is Proportional to Glucose Concentration
2e-
ISIG
Converting ISIG to a Glucose Sensor Value
1
2
 Check glucose
level with a BG
meter
 Enter BG reading
into the insulin
pump or monitor
 Accept BG
reading as a
calibration
3
 The insulin
pump or monitor
calculates
the calibration
factor:
Cal Factor
Meter BG / ISIG
Sensors require calibration using a blood glucose meter
Converting ISIG to Sensor Glucose
ISIG
Meter BG
2e-
Cal Factor = Meter BG / ISIG
108 mg/dL / 10.8 (ISIG) = 10
ISIG
Calibration Factor Examples
Meter BG Glucose / ISIG = Cal Factor
108 mg/dL / 10.8 (ISIG) = 10 (Cal Factor)
10 (Cal Factor) x 10.8 (ISIG) = 108 mg/dL
Cal Factor x ISIG = Glucose
Example: Cal Factor = 10
ISIG
10.8
11.2
12.8
2e-
BG (mg/dL)
108
112
128
calibrated
00:05 min
00:10 min
ISIG = 12.8
11.2