What is Flash Glucose Monitoring?

and more about the Freestyle Libre

Flash Glucose Monitoring measures glucose levels just underneath the skin, and is used by individuals who have diabetes (type 1, type 2 diabetes… anyone who checks their blood glucose regularly). Designed as an alternative to fingerstick monitoring, it performs the same function as a blood glucose meter (that is, it gives you information about your glucose level) however, it does so by “scanning” a glucose sensor, without have to poke through the skin each time you check. The only Flash Glucose Monitoring system available right now (in Canada or anywhere else) is the Freestyle Libre. It’s distributed in Canada by Abbott Diabetes Care, and available through their partner pharmacy (see the Libre website for details).

Share this Article

What Makes Up the Flash Glucose Monitoring System?

The Freestyle Libre system consists of:

1. Sensor:
A sensor is a thin (less than 0.4 mm wide), flexible wire that sits just under the skin (5mm below the surface) and is inserted using an automatic applicator; the sensor is then held in place by an adhesive patch, similar to an insulin pump infusion set or CGM sensor. The sensor is the part of the system that actually measures (“senses”) glucose levels, taking a glucose reading every minute and storing those readings every 15 minutes.
Sensors are disposable: you wear one for 14 days (at which point it automatically stops working) and then throw it out; a new sensor is inserted to begin the next glucose monitoring cycle.

2. Transmitter
The transmitter is integrated into the sensor pod (unlike a CGM transmitter, which is a separate component); as such, it is replaced when the sensor is replaced. The transmitter takes the glucose reading obtained by the sensor and sends it out (via wireless signal) to a separate receiver, called the “reader”.

3. Reader
The reader “reads” the data from the transmitter, and displays the data on-screen. To access the glucose information, you simply “scan” the sensor by placing the reader within 1 cm to 4 cm of the sensor. You don’t even have to pull up your sleeve… the reader can access data readings though clothing (up to 4mm thick).

Tips from the Trenches

You fellow Canadians will be happy to hear that my son can check his glucose using the Libre even while he’s outside building a snowman… the reader worked even through his thick winter coat!

In order to talk to each other, the Libre reader and transmitter need to be quite close because the system uses Near Field Communication (NFC), a secure and highly robust method of transmitting data between two devices, the same technology used by debit or credit card “tap” machines. Unlike Bluetooth (which in its unsecured format is commonly used to transmit from your smartphone to an external speaker, or to the hands-free feature in your car, for example), NFC isn’t subject to “dropped” connections.


What Information is Displayed?

The sensor continuously measures glucose, automatically storing those readings every 15 minutes. Each time the sensor is scanned it automatically transmits data from the last minute, even if that data has not yet been stored.

In addition, scanning prompts the transmitter to send information to the reader about the current glucose reading, as well as those over the past 8 hours (even if you didn’t scan the sensor previously during that time).

As a result, the following information is displayed on the reader screen:

  • Current Glucose Reading (from 2.2 to 27.8 mmol/L. If the sensor reading is less than 2.2, it will display “LO”; if greater than 27.8, it will display “HI”.)
  • Glucose Trend Arrow tells you whether glucose is steady, rising or falling AND how quickly glucose is changing:

glucose is falling quickly
(more than 0.1 mmol/L per minute.


glucose is falling gradually
(between 0.06 and 0.1 mmol/L per minute)


glucose is steady
(not significantly increasing nor decreasing, but is changing slowly, less than 0.06 mmol/L per minute.)


glucose is rising gradually
(between 0.06 and 0.1 mmol/L per minute)


glucose is rising quickly
(more than 0.1 mmol/L per minute.

Glucose trending is critical, because if glucose is 5.5 and falling, that’s very different than if glucose is 5.5 and rising!

      • Graph of Glucose Levels over the Past 8 Hours, for readings up to 21 mmol/L. (See 8 Hours of Back-Data, above.) This graph is helpful as it summarizes and allows you to visually interpret the current glucose reading within the context of recent glucose levels; you can see where you are and where you’ve been, which helps you to decide what to do to best manage current glucose.
      • Number of Operational Days left in your current sensor session. (For example, I just scanned and in the top left corner is the a sensor icon with the message “Ends in 9 days”)
      • Notifications, such as:

      ο  “Low Glucose” if reading is lower than 3.9 mmol/L (independent of the individual target range set).

      ο  “High Glucose” if reading is greater than 13.3 mmol/L (independent of the individual target range set).

      ο  “Glucose Going Low” if glucose is projected to be lower than 3.9 mmol/L within the next 15 mins.

      ο  “Glucose Going High” if glucose is projected to be greater than 13.3 mmol/L within the next 15 mins.

      Using the reader, you can also add digital notes to track food, insulin, exercise, and medication.

      The bottom line on displayed info:

      When making treatment decisions (whether or not take a low treatment or insulin, and how much of either) it’s wise to take 3 factors into account:

      1. the current glucose reading,
      2. the glucose trend (represented by the arrow), and
      3. the glucose graph (which gives background information about your glucose over the last 8 hours).

      Data Storage

      The reader stores about 90 days of glucose data (as long as you replace the sensor every 14 days and scan the sensor at least every 8 hours). So you can use it to view your History of glucose data, including:

      • Logbook = list of your glucose readings, both scanned and fingerstick readings (when the reader is used as a BG meter), as well as blood ketone results (when the reader is used as a ketone tester).
      • Daily Graph = a line graph representing the full 24 hours of sensor readings (not including meter results); you can scroll back through previous days’ data in graph format.
      • Average Glucose = a bar graph of sensor readings for each of four time periods throughout the day, for the past 7, 14, 30, or 90 days (not including meter results). You can see, for example, if your average blood glucose is highest in the morning, or in the evening. This allows you to adjust your blood glucose management strategies to target the most troublesome times of the day.
      • Daily Patterns = a graph that shows the pattern and variability of the glucose readings over a typical day (over the past 7, 14, 30, or 90 days). The median (midpoint) value is shown as a line graph, while the 10 – 90 percentile range is shown as a shaded area around the median line.
      • Low-Glucose Events = the total number of times your glucose dropped below the low threshold (in the past 7, 14, 30, or 90 days)
      • Sensor Usage = how often you scan your sensor, as an average number of “Scans Per Day” that you have performed, as well as the percentage of possible “Sensor Data Captured” from those scans.
      • Time in Target = the percentage of time, across all glucose readings, in which your glucose was “In Target”, “Above” or “Below” you individual target range (for the past 7, 14, 30, or 90 days)

      (Note: The lower and upper thresholds for your target BG range can be set between 3.9 and 10.0 mmol/L. We set ours at 4.0-7.0. When our son was a toddler, his target BG range was 6.0 -10.0. You can set your Libre to whatever target range your child’s diabetes health care team has recommended, within the system’s upper and lower limits.)

      Who can use Freestyle Libre?

      The Abbott website states that “The FreeStyle Libre flash glucose monitoring system is indicated for measuring interstitial fluid glucose levels in adults aged 18 years and older who have at least 2 years of experience in self-managing their diabetes.” Although it is not approved by Health Canada for use by the pediatric population, your child’s doctor can write an off-label prescription for the system if she believes that it will benefit your child, which may allow you to claim the expense through an extended health insurance plan. If you are not concerned whether the expense qualifies under your private health plan, then any adult can order the system without a prescription.


      More on Flash Glucose Monitoring: Pros & Cons of Flash


      Freestyle Libre Flash Glucose Monitoring System User’s Manual, 2017

      This material has been developed from sources that we believe are accurate, however, as the field of medicine (in particular as it applies to diabetes) is rapidly evolving, the information should not be relied upon, as it is designed for informational purposes only. It should not be used in place of medical advice, instruction and/or treatment. If you have specific questions, please consult your doctor or appropriate health care professional.

      Share this Article

      Before Reading This Article…

      If you have not done so already, we recommend that you first read articlus titlus as background information for what follows.