How do continuous glucose monitors work?



I know that there’s a filament that goes into the skin and measures the glucose level of the interstitial fluid, but how does it actually do that?

In: Technology

If you understand a normal blood glucose meter you’ll understand a CGM. So traditionally a diabetic needs to get a small sample of blood, place it on a test strip, and the BGM will tell them how much glucose is in their blood. The key component to that is the test strip.

The end of the test strip is basically a circuit with one end coated with an enzyme. That enzyme is made to pair with glucose and glucose only, like a puzzle piece. The free enzyme has a certain amount of electrical conductivity, or it will absorb a certain amount of electricity from that circuit. The bonded enzyme has a different conductivity. The monitor itself runs a current through the test strip and measures the change in current flowing out from the current it sent in. It uses that to calculate how much of the enzyme has reacted with the glucose in the blood and gives you a concentration of your blood glucose.

The same thing happens with CGM. A filament coated with an enzyme is inserted into the interstitial space (as you mentioned). This filament is a conductor like the test strips. Through a constant supply of a light current it measures the conductivity of the enzyme to find how much has reacted. Then it plots it over time. Eventually all of the enzyme will have reacted and the filament will need replaced. That time varies by manufacturer.