Continuous Glucose Monitoring (CGM)
Continuous glucose monitoring uses a wearable sensor to estimate glucose throughout the day and night. At the practice, CGM readings are reviewed alongside your symptoms, medicines, and daily routine.
CGM adds context to a glucose reading: where it is now, which direction it is moving, and what happens between checks. The aim is to understand patterns and agree on practical changes with your care team, rather than react to every fluctuation.
Your glucose monitoring pathway
Discuss your goals
Review your current treatment, daily routine, glucose records, and questions about high or low readings.
Choose a suitable system
Discuss personal or professional monitoring, device compatibility, wear duration, and costs before starting.
Apply and set up the sensor
Follow device-specific insertion instructions, complete any warm-up, and learn how to view readings.
Record daily context
Note meals, activity, medication timing, sleep, and symptoms to help interpret the glucose trace.
Review the report together
Discuss recurring patterns, time in range, and episodes below or above your agreed targets.
Agree on follow-up
Create a plan for using the information and decide when to review again.
Who it’s for
People with type 1 or type 2 diabetes using insulin, people taking other medicines that can cause low glucose, and others whose diabetes management may benefit from glucose-pattern information. The choice depends on clinical needs, preferences, and the ability to use the device with appropriate support.
How a CGM sensor works
A small sensor filament sits beneath the skin and estimates glucose in interstitial fluid. A compatible reader or phone displays the information. Sensor and blood glucose readings can differ, particularly when glucose changes quickly.
Personal and professional monitoring
Personal CGM and professional CGM serve different purposes. Approved uses, alerts, scanning requirements, and sharing features also differ between individual devices.
| Aspect | Personal CGM | Professional CGM |
|---|---|---|
| Typical use | Ongoing, day-to-day monitoring | A defined assessment period arranged with your care team |
| Reading visibility | Usually visible to you in real time during wear | Depending on the system, may be reviewed only afterwards rather than during wear |
| Alerts and sharing | May include configurable alerts, scanning, and family or caregiver sharing | Typically set up for the assessment period rather than ongoing sharing |
| Best suited for | Day-to-day self-management, especially alongside insulin or hypoglycemia risk | A focused look at glucose patterns before deciding on further changes |
Preparing for your visit
Bring your medication list, recent HbA1c result, available glucose records, and your phone or reader. Tell the team about adhesive reactions and any planned scans or procedures. Ask which sensor, supplies, setup support, and report review are included in the cost.
- Check phone compatibility before purchasing a sensor.
- Ask how long to wear it and when to return.
- Do not change medication or meals solely to improve the report.
Understanding your glucose report
Your glucose report is built from a few key metrics, always interpreted together rather than in isolation.
| Metric | What it shows | Reference note |
|---|---|---|
| Time in Range | The proportion of readings within an agreed glucose band | For many nonpregnant adults, that band is 70–180 mg/dL; pregnancy and individual circumstances may set different targets |
| Time Below Range | How much of the day glucose is below your low threshold | Reviewed alongside your hypoglycemia risk and treatment |
| Time Above Range | How much of the day glucose is above your high threshold | Considered together with Time in Range, not on its own |
| Ambulatory Glucose Profile (AGP) | Multiple days of readings brought together into one recurring-pattern view | Useful for seeing variability and low readings, not just averages |
| Glucose Management Indicator (GMI) | An estimate of average glucose derived from sensor data | Differs from laboratory HbA1c — the two are not interchangeable |
Alerts and finger-prick checks
Agree on alert settings and a response plan with your clinician, and keep a blood glucose meter available.
When to confirm with a fingerstick check
- Symptoms don't match what the sensor shows
- A reading seems unreliable or doesn't fit the situation
- Your device instructions specifically call for a fingerstick confirmation
- Never ignore symptoms while waiting for the sensor reading to catch up
Wearing the sensor day to day
Use only approved application sites and follow the specific device instructions for water exposure, exercise, replacement, and medical imaging. Contact the care team about persistent irritation, a loose sensor, or repeated signal loss. A backup monitoring plan matters when readings are unavailable.
Benefits and limitations
Benefits depend on education, consistent use, and acting on the findings with an appropriate treatment plan.
| Benefits | Limitations |
|---|---|
| Reveals overnight glucose changes that isolated checks miss | Does not diagnose the cause of every glucose change |
| Shows patterns linked to specific meals or activities | Does not replace all finger-prick checks |
| Adds context — direction and rate of change, not just a single number | Does not deliver insulin by itself |
Your follow-up plan
At the review, bring the report and your notes. Discuss repeated patterns before changing treatment. Ask which changes to prioritize, how to assess their effect, and whom to contact between appointments. Monitoring duration and repeat use should match your clinical needs and preferences.
What to expect
Your visit covers suitability, sensor setup, reading the display, and a backup monitoring plan. Wear duration and follow-up depend on the system and purpose of monitoring; confirm these with the practice.
Evidence basis
The ADA Standards of Care in Diabetes—2026 recommend CGM for people with diabetes using insulin, therapies that can cause hypoglycemia, or other treatment where CGM helps management. Device selection and training should be individualized. A blood glucose meter remains necessary as backup.
When to seek care
- Call emergency services for unconsciousness, a seizure, inability to swallow safely, or severe confusion; do not give food or drink by mouth to an unconscious person.
- Seek urgent care for vomiting, abdominal pain, deep or rapid breathing, or marked drowsiness with high glucose or suspected ketones. CGM does not measure ketones.
- Contact your care team for repeated low readings, persistent high readings, or sensor problems that prevent reliable monitoring. Follow your agreed hypoglycemia and sick-day plans.
FAQ
Does CGM replace HbA1c testing?
No. CGM shows daily patterns; laboratory HbA1c gives a longer-term view. Your clinician considers them together.
Can someone with type 2 diabetes use CGM?
Yes. Suitability depends on treatment, hypoglycemia risk, monitoring goals, and individual circumstances, including for some people not using insulin.
Is CGM an insulin pump?
No. It monitors glucose. Only compatible systems linked to a separately prescribed insulin-delivery device can support automated insulin delivery.
How long does a sensor last?
Wear duration and replacement schedules depend on the device. Confirm the exact model and instructions at setup.
Do I still need a glucose meter?
Yes. Keep a meter available for unreliable readings, symptoms that disagree with the sensor, and checks required by the device instructions.
Can I shower or exercise with CGM?
Usually, within your device’s specified limits. Ask about water exposure, sensor adhesion, and your glucose plan around exercise.
Will someone monitor my readings continuously?
Do not assume continuous monitoring by the clinic. Agree on how reports are shared, when they are reviewed, and what to do urgently.
How do I arrange CGM at the practice?
Call or WhatsApp the practice to discuss suitability, sensor availability, costs, and a report-review appointment.
Medical disclaimer: Content on this page is for general education and is not a substitute for individualized medical advice, diagnosis, or treatment. Outcomes vary between patients. Boston Diabetes Center is outpatient / day-care specialty centre with an on-site diagnostic lab and pharmacy — no inpatient beds; imaging and inpatient care are coordinated through partner facilities.