What is continuous glucose monitoring?
CGMs estimate glucose in interstitial fluid and communicate with a supported display. Sampling, transmission and display intervals vary by model; the Stelo app updates every fifteen minutes despite five-minute sensor transmission.
Unlike traditional blood glucose meters that require a finger-stick blood sample to get a single reading, CGM provides a continuous stream of data — showing not just where your glucose is right now, but where it has been over the past hours, and trend arrows that indicate where it is heading.
CGM does not measure glucose in the blood directly. It measures glucose in interstitial fluid — the fluid surrounding cells in tissue just below the skin. This is closely correlated with blood glucose but can lag behind blood glucose during rapid changes (the lag depends on the device and the situation), which is important to understand when interpreting readings.
How does CGM work?
A CGM system has three main components that work together to deliver continuous glucose data to the user.
The sensor
Many CGMs use a filament to sense interstitial glucose; Eversense uses a clinician-inserted optical sensor. Approved wear sites depend on model and age. Do not assume abdominal placement or one sensing chemistry for every CGM.
The transmitter
Attached to the sensor, the transmitter reads the electrical signal from the sensor, applies calibration algorithms, converts it to a glucose value in mg/dL or mmol/L, and transmits the data wirelessly via Bluetooth to a display device. Transmitters are either integrated into disposable sensors or reusable components that attach to each new sensor.
The receiver / app
Supported displays present sensor information. Trends, sharing and alarms differ by model; Stelo and Lingo do not provide clinical high/low alarms.
Wear and warm-up differ: original G7 supports up to 10 days plus 12-hour grace and a 30-minute warm-up; G7 15 Day up to 15 days plus 12 hours and a 60-minute warm-up; original Libre 3 up to 14 days and 60-minute warm-up. Eversense is clinician-inserted and has separate transmitter and calibration requirements.
CGM vs traditional blood glucose monitoring
Traditional self-monitoring of blood glucose (SMBG) using a finger-stick meter has been the standard for decades. CGM does not fully replace it in all situations, but provides a fundamentally different and richer picture of glucose patterns.
| Feature | CGM | Finger-stick meter |
|---|---|---|
| Readings per day | Model-specific sensor and display intervals | Each manual blood sample |
| Trend information | Yes — direction and rate | No — single snapshot |
| Overnight monitoring | Continuous; alarms depend on model | Intermittent measurements |
| Finger-stick required | Calibration and confirmation depend on model | Every measurement |
| Real-time alerts | Model-specific; no clinical alarms in Stelo/Lingo | No continuous alarms |
| Data sharing | Model/app-specific | Logs or supported digital export |
| Cost | Sensor, display and any service costs | Meter, strips and lancets |
| Accuracy in rapid change | Lag varies by model and situation | Capillary blood measurement; meter error also possible |
Even with CGM, finger-stick verification is recommended when CGM readings seem inconsistent with symptoms, before making critical treatment decisions (such as insulin dosing in some circumstances), and when CGM indicates rapidly changing glucose. Always follow your healthcare provider's guidance on when to verify with a finger-stick.
Benefits of continuous glucose monitoring
The clinical evidence for CGM benefits in people with diabetes is substantial and growing. Beyond diabetes management, CGM is revealing new insights about metabolic health in broader populations.
The benefits described above are based on published clinical research in specific patient populations. Individual results vary. CGM is a monitoring tool, not a treatment. Any changes to your diabetes management — including insulin dosing, medication, or diet — should be made in consultation with your healthcare provider.
Who should use CGM?
CGM was originally developed for people with Type 1 diabetes who require intensive insulin therapy. Its indications have expanded substantially and it is now used across a much broader population.
How accurate is CGM?
MARD is the mean absolute relative difference between sensor readings and reference measurements in a particular study. It is an average across paired readings, not an error bound for each reading or a direct clinical ranking across separate studies.
Accuracy depends on the device, glucose range and measurement conditions. A study-wide MARD does not guarantee the accuracy of an individual reading. Follow the current instructions for your specific device and discuss clinical decisions with your healthcare professional. Calibration requirements and any need to confirm readings with a blood glucose meter are device-specific. Follow your current device instructions, including what to do when a reading does not match your symptoms.
Factors that affect CGM accuracy
Rapid glucose changes: Because CGM measures interstitial glucose, it can lag blood glucose during periods of rapid change — such as during or after eating, during intense exercise, or during hypoglycemia; the lag depends on the device and the situation. Trend arrows show the direction of change but are not a universal correction, so follow your device's instructions if a reading does not match how you feel.
Accuracy depends on the device, glucose range and measurement conditions. A study-wide MARD does not guarantee the accuracy of an individual reading. Follow the current instructions for your specific device and discuss clinical decisions with your healthcare professional.
Sensor placement: Accuracy can vary by body site. Follow manufacturer guidelines for approved insertion sites and rotate locations to avoid tissue buildup that may reduce sensor performance.
Certain medications: Some medications, including high-dose acetaminophen (paracetamol), can interfere with CGM accuracy. Check the device's prescribing information for a complete list of potential interferences.
How to get started with CGM
For people with diabetes
Discuss whether CGM is appropriate, the exact model and interpretation with your healthcare professional. Prescription, availability and coverage rules depend on country, product and plan.
For health optimization without diabetes
Several CGM devices are now available over the counter without a prescription in the United States, including Abbott's Lingo and Dexcom's Stelo — both FDA-cleared as over-the-counter medical devices for adults aged 18 and older (Lingo) or people aged 2 years and older (Stelo, since June 2026) who do not use insulin (that includes people without diabetes). These devices are available directly from manufacturers and major pharmacies. They provide continuous glucose data, and medical decisions based on it should involve a qualified healthcare professional.
If you have diabetes or any other medical condition, do not start using a CGM device or make changes to your treatment based on CGM data without first consulting your healthcare provider. CGM data requires clinical context to interpret safely and act upon.
What to expect
Learning to interpret data requires context. Review trends with appropriate guidance, but do not dismiss an isolated low, symptoms or a reading that differs from a blood glucose check; follow device instructions and your care plan.