Knowing what affects your blood glucose (blood sugar) is key to managing diabetes. It can be hard to know what causes your blood glucose to go too high (hyperglycemia) or too low (hypoglycemia). Monitoring your blood glucose lets you be the detective and discover how factors such as food, physical activity, and medications affect you and make changes as needed.
A CGM is a small wearable device that provides readings based on the fluid around your cells (interstitial fluid) and reports these readings as “glucose.” Because these readings are based on interstitial glucose and not blood glucose, the readings will be about 5–15 minutes behind a finger stick blood glucose level. CGMs report glucose regularly throughout the day and show if your glucose is trending up or down.
You will work with your healthcare team to create your glucose goals. For most people, the overall goal is to keep your glucose between 70–180 mg/dL about 70% of the time or more.
Your CGM gives you your glucose when you check it but it also gives you the following:
Time in range: Your time in range graph shows you how much time your glucose was in your target range. It also shows you the percentage of time you were above or below your target range.
Daily graph: The daily graph helps you see if your glucose is in your target range and when your glucose levels went too high or too low. Most CGMs will allow you to personalize your target range.
Trend arrows: Trend arrows can help you quickly see if your glucose is rising or dropping.
Using your CGM to check your glucose regularly will allow you to notice how food, activity, stress, medication, and other factors play a part in how your glucose levels change. With this information, you can work with your healthcare team to make changes to your treatment plan, if needed.
Use the steps below to help you understand your glucose readings.
A good way to see if you’re reaching your goals is to look at your daily graph. Here you can see if your glucose is within your target range and when your glucose levels go too high or too low.
Here’s an example CGM graph staying within the target range of 70–180 mg/dL.
Here’s an example CGM graph of glucose peaking higher than your target range.
Using the glucose readings from your CGM, you can figure out what factors had the biggest effect on your glucose levels. Think about what happened in the hours leading up to an out-of-range reading:
Over time, look for patterns to get an idea of what is regularly affecting your readings.
Once you identify any factors that could have caused your glucose to go too high or low, think about what you can change to help you stay in your target range in the future. Start with a small change to what you eat or physical activity and look at your glucose readings after the change to find out how it affected them.
Example: Looking at his CGM, Chris notices that he is spending more time below his target range than his goal. He looks at his daily graphs over the last few weeks and sees his low values are occurring at nighttime. After chatting with his healthcare team about it, he tries having a bedtime snack with carbohydrates and protein, and this helps him stay in range through the night. He has fewer lows and his time in range increases.
If you’re out of range often, talk with your healthcare team. They can help you decide what changes might help you reach your targets and if your treatment plan needs to be updated.
A CGM can work together with an insulin pump as part of an automated insulin delivery (AID) system to automatically adjust your insulin. If you’re using an AID system, it’s less likely that you’ll find your glucose outside your target range. You can still use your CGM to better understand your glucose trends, help you set and reach goals, and make changes to support your health.
Now that you know how to use your CGM to know what’s affecting your glucose levels, you can learn more about the different factors that can impact your glucose levels.
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