The Ultimate How-To Guide for Using a Continuous Glucose Monitor (CGM)

17 Sep 2025 By Dan Echols, M.D.

The Ultimate How-To Guide for Using a Continuous Glucose Monitor (CGM)

A Continuous Glucose Monitor (CGM) is a game-changer for individuals managing diabetes or those simply keen on understanding their blood sugar levels in real-time. Unlike traditional finger-prick testing, a CGM provides continuous glucose readings, offering valuable insights into how your body responds to food, exercise, stress, and medication. This ultimate guide will walk you through everything you need to know to effectively use a CGM, from understanding the technology to interpreting the data it provides. A Guide To Severe Hypoglycemia What To Do In An Emergency

What is a Continuous Glucose Monitor (CGM)?

A CGM is a small, wearable device that tracks glucose levels throughout the day and night. It consists of a tiny sensor inserted under the skin, usually on the abdomen or upper arm, which measures glucose levels in the interstitial fluid. This sensor sends readings wirelessly to a receiver (a dedicated device or a smartphone) at regular intervals, typically every 5 to 15 minutes. This continuous data stream enables users to see patterns, trends, and fluctuations in their glucose levels, allowing for proactive management of their health.

Why Use a CGM?

Using a CGM offers numerous benefits over traditional blood glucose monitoring:

Real-time Data: Provides a constant stream of glucose readings, eliminating the need for frequent finger-pricks.
Trend Insights: Shows glucose levels in real-time, along with direction and rate of change, allowing for proactive adjustments.
Alerts and Alarms: Warns users of high or low glucose levels, enabling timely intervention and preventing severe fluctuations.
Improved Glucose Control: Empowers users to make informed decisions about diet, exercise, and medication, leading to better glycemic control.
Reduced Hypoglycemia Risk: Alerts can help prevent dangerous low blood sugar events, particularly during sleep or physical activity.
Data Tracking and Analysis: CGM systems record and analyze glucose data, providing valuable insights for healthcare providers to tailor treatment plans.

Choosing the Right CGM for You

The market offers various CGM systems, each with its unique features and benefits. Here are some popular options to consider:

Dexcom G7: Known for its ease of use, accuracy, and smartphone compatibility, Dexcom G7 is a popular choice. It transmits data directly to smartphones and offers customizable alerts.
Abbott FreeStyle Libre 3: This system stands out for its affordability and convenience. It involves a small, disposable sensor and requires scanning with a reader or smartphone to obtain glucose readings.
Medtronic Guardian 4: Integrated with Medtronic insulin pumps, this system offers advanced features such as predictive alerts and automated insulin delivery.

| Feature | Dexcom G7 | Abbott FreeStyle Libre 3 | Medtronic Guardian 4 | | ------------------ | ----------------------------- | -------------------------------- | ----------------------------- | | Data Transmission | Continuous to Smartphone | Scan-based with Reader/Smartphone | Continuous to Pump/Smartphone | | Alerts | Customizable High/Low Alerts | High/Low Glucose Alerts | Predictive and Threshold Alerts | | Sensor Wear Time | Up to 10 days | Up to 14 days | Up to 7 days | | Calibration | Typically No Calibration Required | Optional Calibration | Required | | Integration | Wide Compatibility | Limited Compatibility | Medtronic Pump Integration |

When choosing a CGM, consider factors such as:

Accuracy: Look for systems with a proven track record of accurate glucose readings.
Ease of Use: Opt for a system that is easy to apply, calibrate (if required), and operate.
Compatibility: Ensure the system is compatible with your smartphone or insulin pump, if applicable.
Alerts: Consider the types of alerts offered and whether they meet your specific needs.
Cost: Compare the cost of sensors, transmitters, and other supplies across different systems.
Wear Time: Determine the sensor duration that best fits your lifestyle and preferences.

It’s always best to consult with your healthcare provider to determine the most suitable CGM system for your individual needs and health goals. A1C Test Vs Daily Blood Sugar Check Which Is More Important

Step-by-Step Guide to Applying and Setting Up Your CGM

Once you've chosen your CGM, follow these steps to apply and set it up correctly:

1. Preparing the Site

Choose an Insertion Site: Select a site on your abdomen or upper arm with enough subcutaneous fat. Avoid areas with scars, moles, or tattoos.
Clean the Site: Clean the insertion site thoroughly with an alcohol swab and allow it to air dry completely.

2. Applying the Sensor

Follow the Instructions: Carefully read and follow the instructions provided by the CGM manufacturer. Each system may have slightly different application procedures.
Insert the Sensor: Use the applicator to insert the sensor into the skin. Ensure it is firmly attached and secure.

3. Attaching the Transmitter (If Applicable)

Attach the Transmitter: If your CGM system uses a separate transmitter, attach it to the sensor according to the manufacturer's instructions.
Secure the Transmitter: Ensure the transmitter is securely connected to the sensor to ensure continuous data transmission.

4. Calibrating the CGM (If Required)

Calibrate as Directed: Some CGM systems require calibration with a finger-prick blood glucose reading. Follow the instructions to calibrate your CGM accurately.

5. Setting Up the Receiver or Smartphone App

Download the App: If your CGM system uses a smartphone app, download it from the app store.
Pair the Devices: Follow the instructions to pair the CGM with your receiver or smartphone.
Customize Settings: Configure alerts, alarms, and other settings according to your preferences.

6. Start Monitoring Your Glucose Levels

Warm-Up Period: Allow the CGM to warm up for the specified period (usually 1-2 hours) before relying on the glucose readings.
Monitor Readings: Begin monitoring your glucose levels and observe how they change throughout the day.

Example: Detailed Dexcom G7 Application Process

Clean Site: Use an alcohol swab to clean the chosen application site (abdomen or back of the upper arm).
Remove Applicator Cap: Unscrew the cap of the Dexcom G7 applicator.
Apply Sensor: Firmly press the applicator against your skin. Press the button to insert the sensor.
Remove Applicator: Remove the applicator, ensuring the sensor is securely attached.
Pair Device: Open the Dexcom G7 app on your smartphone and follow prompts to pair with the new sensor.
Warm-Up: Allow the 30-minute warm-up period to complete before using the sensor for glucose readings.

Interpreting CGM Data and Understanding Trends

One of the primary benefits of using a CGM is the wealth of data it provides. Understanding how to interpret this data is crucial for effectively managing your glucose levels.

Key Metrics to Watch

Glucose Levels: Monitor your glucose levels throughout the day and night, paying attention to highs and lows.
Trends: Observe the direction and rate of change of your glucose levels to anticipate potential fluctuations.
Time in Range (TIR): Track the percentage of time your glucose levels are within your target range (typically 70-180 mg/dL for people with diabetes).
Glucose Variability: Assess the degree of fluctuation in your glucose levels, as high variability can increase the risk of complications.
Average Glucose: Calculate your average glucose level over a period to get an overall sense of your glycemic control.

Understanding the Graphs and Reports

Most CGM systems provide graphs and reports that visualize your glucose data over time. Here's how to interpret them:

Glucose Curves: Observe the shape of your glucose curve throughout the day, noting any peaks or valleys.
Trend Arrows: Pay attention to the direction of the trend arrows, as they indicate whether your glucose levels are rising, falling, or stable.
Daily Reports: Review daily reports to identify patterns and trends in your glucose levels, such as how they respond to meals or exercise.
Weekly or Monthly Summaries: Analyze weekly or monthly summaries to assess your overall glycemic control and identify areas for improvement.

Actionable Insights from CGM Data

Using your CGM data, you can make informed decisions about your diet, exercise, and medication:

Identify Trigger Foods: Observe how different foods affect your glucose levels and adjust your diet accordingly.
Optimize Exercise Timing: Determine the best time to exercise to minimize glucose fluctuations.
Adjust Insulin Doses: Work with your healthcare provider to adjust your insulin doses based on your CGM data.
Address Hypoglycemia: Identify the causes of your low blood sugar events and take steps to prevent them in the future.

Example: Interpreting a Glucose Graph

Imagine you review your CGM data and notice the following pattern:

Morning (7:00 AM): Glucose level is 90 mg/dL (within target range).
Post-Breakfast (9:00 AM): Glucose spikes to 180 mg/dL after eating a sugary cereal.
Mid-Morning (11:00 AM): Glucose returns to 120 mg/dL.
Lunch (1:00 PM): Glucose level is 110 mg/dL before eating a balanced lunch.
Post-Lunch (3:00 PM): Glucose rises to 140 mg/dL.
Evening (7:00 PM): Glucose is 85 mg/dL before dinner.

Interpretation:

The sugary cereal caused a significant glucose spike in the morning. Consider replacing it with a lower-carb option.
A balanced lunch resulted in a more moderate glucose increase.
Overall, glucose levels are generally within the target range, indicating good glycemic control.

Troubleshooting Common CGM Issues

While CGMs are generally reliable, issues can arise. Here’s how to troubleshoot common problems: Decoding Your A1C Test Results What Your Numbers Really Mean For Diabetes

Inaccurate Readings:
- Problem: CGM readings consistently differ from finger-prick readings.
- Solution: Ensure the sensor is properly inserted and calibrated (if required). Consider replacing the sensor if accuracy doesn't improve. Check that your hands are clean when you finger-prick. Contaminants on your hands can affect your blood sugar reading.
Signal Loss:
- Problem: The CGM loses connection with the receiver or smartphone.
- Solution: Ensure the receiver or smartphone is within range of the transmitter. Check for interference from electronic devices. Restart the receiver or smartphone. Contact the manufacturer's support if the issue persists.
Sensor Failure:
- Problem: The sensor stops working prematurely or provides error messages.
- Solution: Replace the sensor with a new one. Contact the manufacturer's support for assistance.
Skin Irritation:
- Problem: The sensor site becomes red, itchy, or inflamed.
- Solution: Use a skin barrier wipe before applying the sensor. Rotate insertion sites to avoid overuse of the same area. Consider using a different adhesive bandage.
Alert Issues:
- Problem: Receiving false or missed high/low alerts.
- Solution: Review and adjust your alert settings to ensure they are appropriate for your needs. Ensure the CGM is properly calibrated (if required).

Best Practices for CGM Maintenance

Keep it Clean: Regularly clean the area around the sensor with a damp cloth to prevent infection.
Protect the Site: Secure the sensor with an adhesive bandage to prevent it from dislodging during activities.
Avoid Direct Pressure: Avoid applying direct pressure to the sensor, as this can affect readings.
Stay Hydrated: Drink plenty of water to ensure adequate interstitial fluid for accurate glucose measurement.

Lifestyle Adjustments and Tips for Optimal CGM Use

To maximize the benefits of using a CGM, consider making the following lifestyle adjustments:

Meal Planning: Work with a registered dietitian to create a meal plan that minimizes glucose spikes and promotes stable blood sugar levels.
Exercise Regimen: Consult with an exercise physiologist to develop an exercise regimen that optimizes glucose control.
Stress Management: Practice stress-reduction techniques such as meditation, yoga, or deep breathing to minimize the impact of stress on glucose levels.
Sleep Hygiene: Prioritize adequate sleep to regulate hormone levels and improve glycemic control.
Regular Check-Ups: Attend regular check-ups with your healthcare provider to review your CGM data and adjust your treatment plan as needed.

Enhancing Your CGM Experience

Participate in Support Groups: Connect with other CGM users to share experiences, tips, and support.
Attend Educational Workshops: Enroll in educational workshops or seminars to learn more about CGM technology and diabetes management.
Stay Informed: Keep up-to-date with the latest advancements in CGM technology and diabetes research.
Use Data to Improve: Regularly review your CGM data to identify areas for improvement and fine-tune your diabetes management strategy.

By following this comprehensive guide, you can confidently use a CGM to monitor your glucose levels, gain valuable insights into your health, and make informed decisions to improve your overall well-being. Always consult with your healthcare provider for personalized guidance and support.