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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
Sensor Electrodeinside the needle
Connector to MiniLink or iPro
Body
Introducer Needle Handle
Glucose Sensor Components
Sensor Electrodeinside the needle
Pick up the Sensor on either side of the Connector
Body
Never hold or pick the Sensor up by the needle handle
Introducer Needle Handle
Attaches to the MiniLink Transmitter or iPro Recorder
Connector
Introducer Needle– 22 gauge (1/2 diameter)– Bevel faces down– Discard after insertion
The Sensor Electrode Sits Inside the Introducer Needle
Reference electrode
Counter electrode
Working electrode
Maintaining an Optimal Sensor Placement Ensures Success
Closest to the skin
Layers of the Glucose Sensor
Semi Permeable MembraneSelective to glucose and oxygen
EnzymeThe membrane surrounds a
glucose oxydase enzyme
Electrode
Membrane
Enzyme
Electrode
Outermost Layer of the Glucose Sensor
Semi Permeable MembraneSelective to glucose and oxygen
Enzyme
Electrode
Membrane• Ensures biocompatibility
• Maintains the required glucose to oxygen ratio required for diffusion to the enzyme layer
• Functions as a glucose limiting membrane
The Glucose Sensor Consists of 3 Layers
Semi Permeable MembraneSelective to glucose and oxygen
EnzymeThe membrane surrounds a
glucose oxydase enzyme
Electrode
Glucose and Oxygen Enter Membrane1
Membrane
Enzyme
Electrode
A semi permeable membrane that is very selective to glucose and
oxygen
The Membrane is required for biocompatibility
In subcutaneous tissue
Glucose = 72 to 360 mg/dl
Oxygen = 0.9 mg/dl
Glucose is 5 times more prevalent in subcutaneous tissue
Glucose and Oxygen Enter Membrane1
• 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
• Glucose and oxygen come in contact with the glucose oxidase enzyme
• Glucose and oxygen are converted into Hydrogen Peroxide (H2O2) and gluconic acid
First Chemical Reaction2
Membrane
Enzyme
Electrode
GlyAcidH2O2
Glucose and
Oxygen
• H2O2 seeps through to the Electrode layer
• A voltage is applied to the Electrode, causing H2O2 to breakdown into:
Hydrogen Oxygen 2 electrons
Second Chemical Reaction3
Membrane
Enzyme
Electrode
H2O2
2e-
The more glucose in your body, the more H2O2 generated.
The more H2O2, the more current generated.
The ISIG is Proportional to Glucose Concentration
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
2e-
Membrane
Enzyme
Electrode
ISIG
2
Converting ISIG to a Glucose Sensor Value
Sensors require calibration using a blood glucose meter
1 3 Check glucose
level with a BG meter
The insulin pump or monitor calculatesthe calibration factor:
Enter BG reading into the insulin pump or monitor
Accept BG reading as a calibration
Cal Factor
Meter BG / ISIG
Converting ISIG to Sensor Glucose
ISIG
ISIG
Meter BG
Cal Factor = Meter BG / ISIG
108 mg/dL / 10.8 (ISIG) = 10
2e-
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
BG (mg/dL)2e- ISIG =
calibrated 00:05 min 00:10 min
10.8
108
11.2
112
12.8
12811.212.82e-
112128
