Yes, the FreeStyle Libre is a continuous glucose monitor. The FDA classifies both the Libre 2 and Libre 3 under the same regulatory category: “Integrated Continuous Glucose Monitoring System” (21 CFR 862.1355). That said, there’s a meaningful technical difference between the two versions that has caused some confusion about whether “CGM” is the right label.
Why the Libre Gets Called Two Different Things
Abbott, the company that makes FreeStyle Libre, originally marketed the system as a “Flash Glucose Monitor” rather than a traditional CGM. The distinction came down to how you get your data. With the Libre 2, you have to hold your phone or reader near the sensor to scan it (using NFC, the same tap technology in contactless payments). The sensor doesn’t automatically send glucose readings to your phone. It does use Bluetooth to push alarm notifications, but you still need to scan to see your actual numbers.
The Libre 3 works differently. It streams glucose data continuously to your phone via Bluetooth Low Energy, with no scanning required. Abbott calls this version the “FreeStyle Libre 3 Continuous Glucose Monitoring System,” while the Libre 2 is officially the “FreeStyle Libre 2 Flash Glucose Monitoring System.” Both sit under the FDA’s CGM classification, but the Libre 3 behaves like what most people picture when they think of a CGM: real-time numbers on your phone without any action on your part.
How the Sensor Works
Like all CGMs, the FreeStyle Libre uses a tiny filament inserted just under the skin to measure glucose in interstitial fluid, the liquid that surrounds your cells. This is not the same as blood glucose. Interstitial fluid glucose lags behind fingerstick blood glucose, especially when levels are changing quickly after a meal or during exercise. That lag can be up to 15 minutes but is typically shorter.
In terms of accuracy, the Libre 3 has a mean absolute relative difference (MARD) of 7.9%, based on data from 95 subjects compared against a laboratory reference. In practical terms, 93.2% of its readings fell within 20 mg/dL or 20% of the reference value. A lower MARD means better accuracy, and anything under 10% is generally considered strong performance for a CGM sensor.
What Wearing a Libre Looks Like
The sensor is a small, round disc about the size of two stacked quarters. You apply it to the back of your upper arm using a one-push applicator, and it stays on for up to 14 days. After application, there’s a warm-up period (typically about one hour for the Libre 3) before the sensor begins delivering readings. During those two weeks, you wear it continuously through showers, exercise, and sleep.
You read your data through the FreeStyle LibreLink app (for the Libre 2) or the FreeStyle Libre 3 app. There’s also a companion app called LibreLinkUp that lets a family member or caregiver see your glucose data remotely. Before updating your phone’s operating system, it’s worth checking Abbott’s compatibility guide. Major OS releases from Apple and Android have occasionally caused temporary issues with the apps.
The iCGM Designation
The Libre 3 carries an additional FDA classification as an “integrated continuous glucose monitoring system,” or iCGM. This designation means the device meets specific accuracy standards and, more importantly, is designed to communicate with other digital health devices. An iCGM can potentially connect with insulin dosing apps or automated insulin delivery systems, where the CGM data feeds into software that helps calculate or deliver insulin. The Libre 3 can be used on its own or paired with compatible connected devices where you manually control therapy decisions.
The Libre 2, while still FDA-classified under the CGM regulation, does not carry the iCGM label and lacks this interoperability framework.
Impact on Blood Sugar Management
A large Dutch study (FLARE-NL 5) tracked people with diabetes after they started using the FreeStyle Libre. About 22% of users achieved a clinically significant drop in HbA1c of at least 0.5 percentage points. Among those who did improve, the median reduction was 0.82 percentage points at both 6 and 12 months. That’s a meaningful change: each percentage point drop in HbA1c is associated with substantially lower risk of diabetes complications.
The benefit tends to be largest for people who start with higher A1c levels and who scan frequently. Simply wearing a sensor doesn’t automatically improve glucose control. The value comes from seeing patterns, catching highs and lows in real time, and adjusting food, activity, or medication in response. People who check their data more often generally see better results.
Libre vs. Other CGMs
The main competitor is the Dexcom G7, which also streams data continuously via Bluetooth and carries the iCGM designation. Both have similar accuracy profiles and 14-day or shorter wear periods. The practical differences come down to sensor placement (Libre uses the back of the arm, Dexcom allows the abdomen and other sites), app ecosystem, and which systems they integrate with for automated insulin delivery.
If you’re comparing options, the key question isn’t really whether the Libre “counts” as a CGM. It does, by regulatory definition and by function. The more useful question is whether you want a system that requires scanning (Libre 2, less expensive in some markets) or one that streams automatically (Libre 3, Dexcom G7), and which system your insurance covers or your endocrinologist recommends for your specific setup.