How to Use a continuous glucose monitor (CGM) to Track Blood Sugar
Managing diabetes involves more than checking blood glucose at a few points during the day.
Your glucose levels can fluctuate depending on food, activity, sleep, stress, medication and many other things. Learning more about this can give you and your healthcare team some insight into making informed decisions about your diabetes and lifestyle choices.
A continuous glucose monitor will give you an insight into how your glucose levels are behaving throughout the day.
Rather than measuring glucose levels from a small drop of blood, like a traditional blood glucose meter does, it has a sensor that goes underneath your skin. This estimates your glucose levels based on how much glucose is present in the interstitial fluid around your cells.
It can give you useful insights into patterns you may have such as post meal highs, lows, overnight fluctuations and activity related responses. You can also get useful data such as time in range, time above range, time below range and glucose variability.
However, using a CGM involves more than watching the numbers change. It is important to understand what the readings mean, recognize the device’s limitations and know when a result needs attention.
This guide explains how continuous glucose monitoring works, how to understand your glucose graphs and trend arrows, how to use CGM alerts safely and how to look at CGM reports.
Medical Note: The information provided in this article is for general information purposes only. It should not be used as a substitute for personalized medical advice. Insulin dosages should not be altered based on CGM data, nor should medication for diabetes be discontinued. Always follow the information provided in your device and treatment plan given by your healthcare professional.
Article Index
- What Is a Continuous Glucose Monitor?
- How Does a CGM Measure Blood Glucose?
- Who Can Benefit from Using a CGM?
- Getting Started: How to Use a CGM
- Understanding CGM Readings and Target Ranges
- How to Read CGM Graphs and Trend Arrows
- How to Use CGM Alerts Safely
- Using CGM Data to Understand Food and Meals
- How Physical Activity Affects CGM Readings
- How Sleep and Stress Influence CGM Patterns
- How to Review Weekly CGM Reports
- Common CGM Mistakes to Avoid
- CGM Limitations and When to Use a Finger-Stick Test
- Frequently Asked Questions
- Key Takeaways
- References
What Is a Continuous Glucose Monitor?
A continuous glucose monitor (CGM) is a wearable device that can estimate your glucose levels throughout the day and night.
The device contains a small sensor that is inserted underneath the skin. The sensor is usually placed under the skin at an approved site, such as the arm or abdomen, depending on the device. The sensor will measure glucose levels in the interstitial fluid, which is the fluid found around cells.
Depending on the model, updated glucose readings are sent to your smartphone, receiver or compatible insulin delivery device every few minutes.
Unlike traditional blood glucose testing, the CGM provides a series of readings. This can be viewed as a trend.
This can help those with diabetes and their healthcare team to identify:
- When glucose levels are rising after meals.
- When glucose levels are dipping below target.
- Changes in glucose levels while sleeping.
- Trends relating to physical activity.
- When glucose levels are consistently high or low.
- How glucose levels are responding to prescribed treatment.
For example, someone may notice that their glucose levels are consistently rising after breakfast but are more consistent after lunch. Or someone may notice that their glucose levels tend to dip when they are being physically active for longer periods of time.
These observations can provide useful information for reviewing meals, medication and daily routines.
A CGM is not a treatment for diabetes. However, it can help you understand glucose trends and discuss appropriate management strategies with your healthcare professionals.
How Does a CGM Measure Blood Glucose?
Although CGM is commonly described as continuous blood glucose monitoring, most systems estimate glucose levels in the interstitial fluid rather than measuring blood glucose directly.
Typically a CGM will have three parts:
Sensor
A small device that goes under your skin. This detects glucose levels in the interstitial fluid around it.
Transmitter
The transmitter sends the data collected by the sensor to a compatible receiver or phone. Some newer CGM systems have the transmitter built into the sensor.
Receiver/Phone App
This will show you your glucose readings, graphs, trend arrows and alerts. Many devices will give you reports to help you understand how your glucose has been behaving over the last few days.
Why Can CGM Readings Differ from Blood Glucose Measurements?
There can be a discrepancy between blood glucose levels and interstitial glucose levels.
If there is a rapid change in your blood glucose levels it can take several minutes for the interstitial glucose levels to catch up.
For example if you have eaten a high carbohydrate meal your blood glucose levels may start to rise but your CGM may not yet have picked up on the full change.
This can also happen during exercise or after taking insulin.
This can cause discrepancies between your CGM and finger stick.
However it is important to understand this so that you don’t get unnecessarily worried about discrepancies.
The Centers for Disease Control and Prevention (CDC) provides further information about how continuous glucose monitors work.
Who Can Benefit from Using a CGM?
Continuous Glucose Monitoring can be beneficial for providing more detailed insight into your glucose profile.
The American Diabetes Association’s 2026 Standards of Care recommend offering CGM to people with diabetes who use insulin, those taking non-insulin medications that can cause hypoglycemia, and others whose diabetes management would benefit from this technology.
Some examples include:
People with type 1 diabetes
Provides you with insight into the changes in glucose throughout the day and night. It can help with managing insulin and can identify when glucose levels are dropping/rising.
People with type 2 diabetes
Those who are using insulin or particular glucose lowering drugs can benefit from having continuous monitoring. This can be especially helpful if your blood glucose levels are frequently changing or if you are regularly getting hypoglycemia.
It can also be useful for some non-insulin users with type 2 diabetes.
People who experience frequent hypoglycemia
Alerts can help to give you earlier indication that your glucose levels are starting to drop or are in the lower range. This can help you stick to your individual hypoglycemia management plan.
People with impaired awareness of hypoglycemia
Some people have poor awareness of hypoglycemia meaning they don’t get the typical warning signs. Continuous glucose monitoring alerts can provide extra information but will not guarantee detection and prevention of all episodes.
People who need more detailed glucose information
Some people can benefit from knowing how their glucose levels are changing throughout the day, for example after a meal, during exercise or at night. A CGM can help you see patterns that may not be picked up by the occasional finger stick.
However, it may not be necessary for everyone with prediabetes, insulin resistance or those interested in their metabolic health. It depends on the individual’s medical situation and why they want to use it.
Choose a CGM system that suits your needs, preferences, treatment requirements, availability and cost.
Getting Started: How to Use a CGM
To get the most out of your CGM you’ll need to set it up properly. Training and understanding the device will help you get useful information.
Below is a general guide – different brands will have different steps for where to place the sensor, turning it on, warming up and how to use it.
Step 1: Choose an Appropriate CGM System
Different CGM systems have different features.
Some provide automatic real-time readings, while others require users to scan the sensor or use a compatible device to retrieve readings.
Before selecting a system, consider:
- Whether it provides automatic readings.
- How glucose alerts are configured.
- Whether it connects to a smartphone.
- How long each sensor is designed to last.
- Whether it can integrate with other diabetes technology.
- The availability and cost of replacement sensors.
- Whether the system is appropriate for your treatment needs.
A healthcare professional can help identify which device is suitable.
Step 2: Follow the Manufacturer’s Sensor Instructions
Each CGM has specific instructions about where and how the sensor should be applied.
The recommended location can differ between devices and age groups.
Follow the manufacturer’s instructions concerning:
- Approved sensor placement.
- Skin preparation.
- Sensor insertion.
- Adhesive application.
- Sensor activation.
- Warm-up periods.
- Replacement schedules.
Avoid placing the sensor in an area that is likely to experience repeated pressure or friction.
Step 3: Connect the Sensor to the Receiving Device
Depending on the system, readings may be transmitted automatically to a smartphone or dedicated receiver.
Check that:
- The device is compatible with the CGM.
- Bluetooth or other required connectivity is enabled.
- The correct application is installed.
- The sensor is successfully paired.
- Notifications are enabled where appropriate.
Some devices require users to scan the sensor rather than receiving automatic updates.
Step 4: Learn the Main Features
Before relying on the device, become familiar with its main functions.
These may include:
- Current glucose reading.
- Trend arrows.
- Recent glucose history.
- High and low alerts.
- Time-in-range reports.
- Sensor status.
- Data-sharing options.
Knowing how these features work can make the information easier to interpret.
Step 5: Wear the Sensor According to Instructions
Use the sensor for the period specified by its manufacturer.
Check the device regularly for sensor errors, missing readings or adhesive problems.
If the sensor comes loose, is faulty or causing any discomfort, follow the manufacturer’s instructions.
Step 6: Review Your First Several Days of Data
Learn how your glucose levels are behaving during the first stage.
Notice any patterns relating to eating, exercise, sleeping and medicines.
Do not make any large changes to your diet or medicines due to an outlying value.
We want you to gain an understanding of the data and be able to have meaningful conversations with your healthcare team about any patterns.
Understanding CGM Readings and Target Ranges
Understanding what the readings mean is one of the most important parts of using a CGM.
Glucose can be measured in mg/dL (milligrams per deciliter). Some devices measure it in mmol/L (millimoles per liter).
For many nonpregnant adults with diabetes, a commonly used target glucose range is:
- Lower boundary: 70 mg/dL (3.9 mmol/L).
- Upper boundary: 180 mg/dL (10.0 mmol/L).
However, this is a general clinical reference range rather than a universal target for every individual.
Your age, whether you are pregnant, what type of diabetes you have, your treatment, any medical conditions and your risk of hypoglycemia can all impact on what your blood glucose targets should be.
What Is Time in Range?
Time in range refers to the percentage of time that blood glucose stays within the target range.
The ADA identifies more than 70% time in range as a commonly used target for many nonpregnant adults with diabetes.
This is equivalent to approximately 16 hours and 48 minutes in range over a 24-hour day.
For instance, if you spend 75% of your day in range you will have spent around 18 hours in range.
However, a higher time in range should not be pursued at the expense of frequent low-glucose episodes.
Other Important CGM Measurements
Time Above Range (TAR)
This represents the percentage of time glucose levels remain above the specified target range.
For the commonly used adult range, this means glucose readings above 180 mg/dL.
Time Below Range (TBR)
This represents the percentage of time glucose levels fall below the specified target range.
Readings below 70 mg/dL are important because they may indicate hypoglycemia.
Readings below 54 mg/dL represent a more significant level of low glucose.
Glucose Management Indicator (GMI)
GMI is an estimate calculated from average CGM glucose readings. It can help users and healthcare professionals interpret glucose patterns, but it is not the same as a laboratory HbA1c result.
Glucose Variability
Glucose variability describes how much glucose levels fluctuate over time.
Even if you have an average blood glucose level it could be that it is fluctuating quite a lot throughout the day.
By looking at these figures as a whole you get a better overall picture.
Why Time in Range Matters
Consider two people with similar average glucose levels.
Person A could be spending a large amount of time in range with limited spikes.
Person B, however, may have regular high readings post meal and the odd low reading at night.
Both may have the same average glucose readings but will have different patterns throughout the day.
Using time in range and other CGM metrics can help us identify these.
Work with your healthcare professional to establish appropriate individual targets.
How to Read CGM Graphs and Trend Arrows
A CGM graph can show changes in your glucose levels throughout the day.
This will give you more information than a single reading. You’ll be able to see what direction your glucose is moving in.
Most systems use arrows to show if your glucose is stable, increasing or decreasing.
Different companies use different symbols so it’s best to refer to your device instruction manual.
Understanding Common Trend Patterns
Stable glucose
A relatively flat trend indicates that glucose levels are changing slowly or remaining fairly stable.
Gradually rising glucose
A rising trend may occur after a meal or during periods of reduced insulin availability.
It is useful to consider the timing of meals, activity and medication rather than automatically responding to the reading.
Rapidly rising glucose
A rapidly rising trend may indicate a more substantial change.
However, a trend arrow alone does not determine whether additional insulin, exercise or another intervention is appropriate.
Gradually falling glucose
A downward trend may occur during physical activity, after medication or between meals.
People using insulin or medications that can cause hypoglycemia should pay particular attention to their individualized safety instructions.
Rapidly falling glucose
A rapidly falling trend deserves attention, particularly when glucose is approaching the low range or symptoms are present.
Follow the hypoglycemia management plan provided by your healthcare professional
Example: Understanding a Post-Meal Glucose Pattern
If you notice that your glucose levels tend to rise after breakfast, instead of immediately eliminating a particular food, you could record:
- What you ate.
- Your approximate meal portion.
- When you ate.
- Your medication timing, if relevant.
- Your physical activity.
- How your glucose pattern changed afterwards.
This can help create an overall pattern.
This can then be discussed with your healthcare professional or registered dietitian.
The main point of having a graph from your CGM is to see patterns rather than being tempted to get too caught up in every fluctuation.
How to Use CGM Alerts Safely
CGM alerts are useful as they inform you that your glucose has reached a certain level, or is changing quickly.
This can help you to identify potential issues.
Some common alert types include:
- Low glucose
- High glucose
- Glucose going up quickly
- Glucose going down quickly
- No signal
- Sensor alerts.
Setting High and Low Glucose Alerts
There is no one-size-fits-all setting for alerts.
They should be based on:
- The individual’s blood glucose targets
- Type of diabetes
- Whether you’re using insulin/medication
- History of hypoglycemia
- Blood glucose overnight
- Treatment recommendations for the individual
For example if you experience repeated overnight hypoglycemia regularly your alerts will need to change compared to someone that is worried about high blood glucose lasting a long time.
Discuss appropriate alert settings with your healthcare professional.
What to Do When an Alert Appears
When you receive a notification:
- Check your blood glucose
- Look at the trend data.
- Consider whether the reading matches how you feel and any symptoms you are experiencing.
- Use your personalized diabetes action plan.
If your symptoms do not match what the CGM is showing or the device says you should confirm then confirm with a finger stick.
Speak to your healthcare team if you are getting any unexpected alerts.
If hypoglycemia is confirmed or strongly suspected, follow your prescribed hypoglycemia treatment plan promptly.
Do not take additional insulin, skip meals or change prescribed medication simply because of a temporary change in the graph.
People using insulin should follow their prescribed correction plan and not make up doses based on trend arrows.
Avoiding Alert Fatigue
Too many alerts can be a source of frustration.
This is often referred to as ‘alert fatigue’.
Frequent notifications may cause users to become overwhelmed or overlook important alerts.
To make sure you are not getting too many alerts:
- Talk to your health care professional about what level of alerts would be appropriate for you.
- Only use the alerts that are relevant to your treatment.
- Understand the difference between urgent and informational alerts.
- Don’t switch off any important safety alerts.
The American Diabetes Association emphasizes the importance of appropriate training when people start using diabetes technology.
Using CGM Data to Understand Food and Meals
Meals can produce noticeable changes in blood glucose levels.
Carbohydrates generally have the most immediate effect on post-meal glucose levels. However, the response also depends on portion size, meal composition, medication, physical activity and individual metabolism.
A meal high in refined carbohydrates may produce a different glucose response from a meal that combines carbohydrates with protein, fiber and healthy fats.
A CGM can help investigate questions such as:
- Does glucose repeatedly increase after a particular breakfast?
- Are larger portions associated with higher post-meal readings?
- Do different carbohydrate sources produce different patterns?
- Does meal timing influence glucose changes?
- Are the results consistent across several days?
Comparing Different Meal Patterns
Consider two hypothetical breakfasts.
Breakfast A
Large bowl of refined cereal with sweetened beverage.
Breakfast B
Smaller bowl of whole-grain cereal with plain yogurt and nuts.
These options could have different effects on blood glucose levels due to differing carbohydrate amounts and protein, fats and fiber.
However, individual responses vary, and no single meal produces the same glucose pattern in everyone.
The purpose of comparing meals is to understand personal patterns rather than label every temporary glucose increase as harmful.
Keep a Food and Glucose Record
Many CGM applications allow users to record meals, activity and other observations.
A simple record can include:
- Meal time.
- Main foods consumed.
- Approximate carbohydrate intake, if advised.
- Glucose readings before and after eating.
- Physical activity.
- Relevant medication information.
Over time, this information may help identify recurring patterns that can be discussed with a healthcare professional or registered dietitian.
A balanced eating pattern remains important. CGM readings should not encourage unnecessary food restriction or the elimination of nutritionally valuable foods.
How Physical Activity Affects CGM Readings
Exercise can have an effect on glucose levels.
During many forms of moderate aerobic exercise, working muscles use glucose for energy, which can contribute to a decrease in blood glucose.
Some people may also experience lower glucose levels for several hours after physical activity.
However, high intensity exercise can sometimes cause a temporary rise in glucose due to stress hormones being released.
The response depends on:
- Exercise intensity.
- Duration of activity.
- Starting glucose level.
- Insulin availability.
- Medication.
- Recent meals.
- Individual health conditions.
What Can CGM Data Reveal About Exercise?
A CGM may help identify patterns such as:
- Glucose decreases during longer walks.
- Delayed glucose reductions after exercise.
- Temporary increases during intense workouts.
- Differences between morning and evening activity.
- Changes associated with different exercise routines.
You might notice that a regular walk after eating leads to a more moderate post-meal glucose pattern.
This information may be useful, but people using insulin or medications that can cause hypoglycemia should discuss exercise-related glucose management with their healthcare professional.
Exercise should not automatically be used to correct a high glucose reading. This will depend on your condition, how you are feeling, what your medications are and your treatment plan.
How Sleep and Stress Influence CGM Patterns
Sleep patterns and stress are important factors to consider.
Poor sleep, irregular sleep schedules and psychological stress may influence hormones involved in glucose regulation.
This can be different for each individual.
Sleep and Overnight Glucose Patterns
Some people will notice an increase in their blood glucose levels due to poor sleep during the night.
Others may have regular drops in the night related to medication, eating and exercise.
Looking at CGM data can help identify these trends.
When reviewing overnight readings, consider:
- Bedtime meal timing.
- Evening physical activity.
- Prescribed medication.
- Sleep duration.
- Repeated overnight alerts.
- Sensor placement and possible pressure on the sensor.
What Are Compression Lows?
Compression lows are caused by the pressure placed upon the CGM sensor.
This can occur if the person is sleeping directly onto the sensor.
This can create a sudden drop on the graph that may not reflect an actual decrease in blood glucose.
If you have an unexpected low overnight, and you are not experiencing any symptoms, you should consider if it could be due to pressure being applied to the sensor. Always follow the instructions for your device. If applicable, use a finger stick.
Not all overnight lows will be caused by a compression artifact. Hypoglycemia should still be taken seriously.
Stress and Glucose Changes
Hormonal factors can affect your glucose levels.
You may notice that your numbers are higher during times of high stress.
Keeping notes about sleep, stress and daily routines may help you identify recurring patterns.
For further reading, see our article on how optimizing sleep duration may improve insulin sensitivity.
How to Review Weekly CGM Reports
An advantage of using a CGM is that it allows you to see trends over several days.
This means that users can look at reports to see patterns.
Many systems have a standard report called an Ambulatory Glucose Profile (AGP) which shows trends over several days.
What Should You Look for in a CGM Report?
Important measurements include:
Average glucose
This shows the average of the recorded glucose readings during the reporting period.
Time in range
This indicates the percentage of time glucose remains within the selected target range.
Time above range
This shows how much time glucose spends above the target.
Time below range
This identifies the percentage of time glucose remains below the target.
Glucose variability
This describes how widely glucose readings fluctuate.
Glucose Management Indicator
GMI provides an estimate based on average CGM glucose. It should not be treated as an exact replacement for laboratory HbA1c.
How Much CGM Data Is Useful?
The ADA’s 2026 Standards of Care describe a 10- to 14-day CGM assessment, with at least 70% active sensor data, as useful for evaluating glucose patterns and time in range.
This is a commonly used method of assessment.
It does not mean that everyone will have to wait 14 days to look at their alerts and low glucose events.
Safety alerts and treatment guidance remain important throughout sensor use.
Questions to Consider During a Weekly Review
When reviewing your report, consider the following questions:
- Have your glucose levels been falling below the target range?
- Do your glucose levels repeatedly increase after particular meals?
- Do your overnight readings show a consistent pattern?
- Does physical activity appear to affect your glucose levels?
- Are you experiencing frequent high or low readings?
- Is there sufficient sensor data to understand your overall glucose patterns?
- Have you experienced any changes in medication, health or lifestyle?
The aim of looking through the report is to identify any useful observations to discuss with the healthcare team.
Medication and insulin changes should be made following an individualized care plan.
Common CGM Mistakes to Avoid
CGMs provide useful information, but misunderstanding the readings can cause unnecessary concern or inappropriate decisions.
Common mistakes to avoid include:
Reacting to Every Small Glucose Change
It is normal for your glucose to vary.
A short-term increase in your glucose after eating does not necessarily mean there is a problem.
Look for trends.
Focusing Only on the Current Reading
One reading will not give you all the information you need.
You might want to consider what direction and how fast your glucose is moving, what you have been doing recently and any symptoms.
Assuming CGM Readings Always Match Finger-Stick Results
CGMs measure glucose found in interstitial fluid whereas traditional meters measure glucose in the blood.
There can be discrepancies between measurements, especially if your glucose levels are fluctuating.
Ignoring Low-Glucose Alerts
Do not ignore low glucose alerts, especially if you take insulin or medication which can cause hypoglycemia.
If you are experiencing frequent low glucose follow your treatment plan and talk to a medical professional.
Changing Medication Without Medical Guidance
You cannot look at your CGM graph to work out the correct amount of insulin or medication to take.
If you change your treatment without medical advice this could cause serious glucose fluctuations.
Setting Too Many Notifications
Too many alerts can cause alarm fatigue.
Set your alerts to suit your needs. Do not turn off any important alarms without talking to your healthcare professional.
Overlooking Sensor Problems
Sensor problems, missing readings, poor adhesion and pressure on the sensor can affect the information displayed.
Follow the manufacturer’s instructions to troubleshoot any issues with your device.
Treating Every Food-Related Increase as Harmful
Some increase in glucose after eating is a normal physiological response.
The aim of managing diabetes is to safely reach your individual clinical goals.
CGM Limitations and When to Use a Finger-Stick Test
However, there are limitations with CGM technology.
The sensor measures interstitial glucose, which may not be the same as the blood glucose level.
There are several other factors that can influence the readings shown:
- Rapid glucose changes.
- Sensor insertion issues or sensor malfunction.
- Pressure on the sensor.
- Interference with particular devices or medications, depending on the CGM model.
- Device-specific limitations.
When Should You Use a Finger-Stick Blood Glucose Meter?
A conventional blood glucose meter remains an important backup and confirmation tool for people using CGM.
A finger-stick measurement may be needed:
- When symptoms do not match the CGM reading.
- When a reading seems unexpected or unreliable.
- When the device displays an error or missing data.
- When the manufacturer’s instructions recommend confirmation.
- When a clinician has advised confirmatory testing.
- During certain periods of rapid glucose change.
Wash and dry your hands before testing. Follow the manufacturer’s instructions for the meter.
The American Diabetes Association recommends that people using CGM also have access to blood glucose monitoring equipment.
Does a CGM Replace HbA1c Testing?
No.
A continuous glucose monitor (CGM) provides information on your glucose levels during the time you are wearing the sensor.
HbA1c is a laboratory test that reflects average blood glucose levels over approximately two to three months.
Both can provide helpful information.
The data provided by the CGM can be helpful if your HbA1c does not give a complete picture of your glucose levels.
When Should You Seek Medical Advice?
If you are having any of the following issues with your CGM, please contact your healthcare professional:
- Repeated high readings.
- Frequent low-glucose alerts.
- Unusual overnight patterns.
- Symptoms inconsistent with readings.
- Repeated sensor issues.
- Issues understanding the reports.
Severe hypoglycemia, loss of consciousness, seizures or an inability to swallow require emergency assistance. Do not give anything by mouth to someone who is unconscious or unable to swallow.
For further information about conventional blood glucose monitoring, consult the FDA’s guidance on blood glucose monitoring devices.
Frequently Asked Questions
What is the best way to use a CGM for diabetes management?
Use the device correctly and understand what the readings mean and the trend arrows. Discuss recurring patterns with your healthcare professional rather than independently changing your medication.
How often should I check my CGM?
Most CGMs will update automatically every few minutes. You do not have to check each reading. However, you should pay attention to any important alerts and look at the longer term reports as per your device instruction and advice from your healthcare team.
What is a good time-in-range target?
A common target for many nonpregnant adults with diabetes is more than 70% of readings between 70 and 180 mg/dL. However, this target can vary depending on age, health, pregnancy and hypoglycemia risk.
Can a CGM prevent low blood glucose?
CGM alerts can help identify falling glucose levels but cannot guarantee that hypoglycemia will be prevented. Always follow your prescribed hypoglycemia management plan.
Why is my CGM reading different from my glucometer?
CGMs measure glucose in the interstitial fluid whereas traditional meters measure blood glucose. This can lead to differences in readings particularly when glucose levels are changing rapidly. If your symptoms do not match the CGM then please follow the device instructions and confirm with a finger stick.
Can people without diabetes use a CGM?
Some people without diabetes use CGMs, although routine monitoring is not necessary for everyone. Whether CGM provides benefits for people without diabetes or those with prediabetes depends on the clinical situation and reason for monitoring. Discuss potential benefits, limitations and costs with a healthcare professional.
Should I change my insulin dose based on CGM trend arrows?
You should only follow specific advice given by your diabetes care team for adjusting your insulin. Trend arrows should not be used to create your own correction doses.
How long should I wear a CGM before reviewing the results?
CGMs are designed for continuous use. The length of time will depend on the sensor itself. For clinical assessment, 10–14 days of CGM data with at least 70% active sensor time is commonly used when sufficient data are available.
Can a CGM show why my blood glucose increases after eating?
CGMs will show you when your glucose levels rise and for how long, but cannot give you the exact reason why on its own. This can depend on what you have eaten, how much, medications, physical activity, stress and other factors.
Why does my CGM show low glucose while I am sleeping?
This could be due to genuine nighttime hypoglycemia, medication or compression of the sensor. Compression can cause misleading readings. Confirm unexpected readings when appropriate, particularly when symptoms do not match the CGM reading or the device instructions recommend confirmation.
Key Takeaways
A continuous glucose monitor provides detailed information about glucose patterns throughout the day and night.
It can help people with diabetes understand how meals, physical activity, sleep, stress and prescribed treatment relate to glucose changes.
Reviewing time in range, time above range, time below range, glucose variability and recurring patterns can provide a more complete picture than focusing on individual readings.
However, CGMs have limitations. Because they estimate glucose in interstitial fluid, readings may differ from finger-stick blood glucose measurements, particularly when glucose levels are changing rapidly.
Glucose targets, alert settings and treatment decisions should be individualized. People using insulin or other medications that can cause hypoglycemia should follow their prescribed treatment plans and discuss recurring patterns with their healthcare team.
When used appropriately, a CGM can support more informed diabetes management. It is a monitoring tool, not a replacement for prescribed medication, professional advice or routine medical care.
References
- American Diabetes Association. Diabetes Technology: Standards of Care in Diabetes—2026.
- American Diabetes Association. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes—2026.
- Centers for Disease Control and Prevention. Continuous Glucose Monitors.
- Battelino T, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care. 2019.
- S. Food and Drug Administration. Blood Glucose Monitoring Devices.
- American Diabetes Association. Standards of Care in Diabetes—2026.
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