how does freestyle libre work

How does Freestyle Libre work

I’ve been wearing a Freestyle Libre for over 3 years now and I can say unequivocally that this technology is a game changer and a fascinating piece of kit that actually makes you healthier and more in tune with your metabolism and blood sugars.

How does the Freestyle Libre sensor attach? 

In short…it’s pretty easy.  In the Libre kit you get:


  • A sensor pack (contains the actual glucose sensor that sticks to your skin)
  • A sensor applicator (applies the sensor to your skin)
  • An alcohol wipe – prepares the skin pre-application

how does freestyle libre work

The recommended location to apply is the back of either arm.  Although you will find that many Libre users apply in other locations dependent upon their needs and preferences.  I have always used the back of my left triceps (see image).


The sensor pack and applicator attach to each other and this inserts the sensor into the applicator ready for attachment to your body.  I recommend setting the sensor pack on a flat surface and pushing the applicator down into the sensor pack.  This minimizes risk of attachment issues.


Then clean the skin, place the applicator in the area you want to apply to and press down.  This injects the sensor into your arm.  I hold it for a few seconds to ensure adhesion.


Tip: I apply a new sensor 60 minutes prior to the old sensor running out and use my Libre scanner to srt the new sensor and keep the old sensor linked to my iPhone app.  This helps me avoid the one hour lag and calibration time so I have no gap in my readings. I apply the new sensor right next to the old one on the same arm.


Does it have a needle? 


It does have a rather scary looking needle.  The needle houses the filament that is inserted in the skin.  The needle is the delivery mechanism for the filament.  It gets the filament into the skin and then the needle comes out, leaving the filament left behind.  It may look scary but in truth 95% of the time there is no pain.


Does it hurt? Is it painful?


To reiterate…there is rarely any pain.  On random occasions there’s a sting and even a little blood.  But I can’t remember the last time I had pain or blood.


How does it read your sugar level?


This is the fun part.  The filament contains an enzyme called glucose oxidase, this enzyme reacts with the interstitial fluid, converts glucose to hydrogen peroxide.  A current is then generated which is electronically transmitted to your reader or smartphone app.

For a more detailed scientific understanding on how does the sensor measure glucose here’s one of many articles that digs deeper.

It’s important to note that this is an interstitial reading not a blood reading.  It is a proxy for a blood reading.  It’s good enough for me.

Diagram courtesy Abbott


How much does the Libre CGM costs


May vary from country to country but in general terms you’re looking at $75 USD to $80 USD per sensor and a sensor lasts 14 days.  Assuming you protect it with one of our patches for freestyle libre sensor.


How to cover Freestyle Libre sensor (with patches)


This is most definitely in our wheelhouse here at Not Just a Patch.  Firstly, in my experience, I 100% need to protect my Libre.  Guaranteed it comes loose by day 14 without a doubt.  A full coverage patch for Libre is useful and will prevent sensor loss which can be costly.  Especially when exercising, in particular swimming and yoga.  A question that comes up regularly is “can I cover the hole” in the Libre.  There is some confusion around this one.  NJaP Patches are made of cotton, the same as your clothing.  For this reason, there is no problem covering the Libre with NJaP.  In reality, there is really very little issue with covering the hole and of the thousands of people wearing NJaP there’s never been any problems. 


This article was medically reviewed by Rachael Baker (BNg; CDE; MNgPrac)