Continuous Glucose Monitors: Are They a Game-Changer or Just Hype?

Do you ever feel super frustrated when your CGM reading doesn’t match your finger stick? Fun fact: It’s normal to notice differences between your CGM readings and a finger stick. A Continuous Glucose Monitor (CGM) is a powerful tool. Read more to learn how to get the most out of your CGM.

Understand How It Works

CGMs measure interstitial fluid, not blood. While finger sticks measure glucose directly in your blood, CGMs measure the glucose (sugar) level in the fluid surrounding your cells (interstitial fluid). Because of this, there’s a natural time lag. CGMs can be about 5-15 minutes behind a finger stick reading because glucose takes time to move from the bloodstream to the interstitial fluid. This is why you want your blood sugar to be steady when you compare.
Each CGM system has different parameters for accuracy. Most are factory-calibrated, but some brands will still allow or require a finger stick calibration. Following the manufacturer’s instructions is key to making sure you are using a correctly-calibrated CGM. Finger sticks are still the gold standard for confirmation. If your CGM reading feels “off,” or seems impossible, double-check with a fingerstick, especially for treatment decisions like insulin/medication dosing.

Sensor Placement Matters

Be sure to place your CGM in a location that is recommended by the manufacturer for best performance. Locating it elsewhere on your body can change the readings and affect accuracy. You should avoid areas with scarring or irritation, or the side where you commonly sleep to avoid false low-sugar alerts caused by compression of the sensor.

Setting Alerts

Most modern CGMs allow you to set alerts for the low and high end of your desired range. You must know what a healthy range is for you before you start using your CGM. Your healthcare professional can help determine what a healthy range goal should be for you. When you first begin, start with a conservative range, and then adjust as you acclimate to the device and the reliability of the information it provides. For example, you might start out with your range set at 80mg/dL for a low and 180mg/dL for a high. After getting used to it, you might decide that you can either loosen or tighten up that range as you are comfortable. Remember, too, that experiencing too many alerts can cause alarm fatigue–causing you to perhaps ignore an important alert.

Data Gaps and Unexpected Readings

Technology is a tool, right? Well, tools are not infallible. With a CGM, you might experience your sensor losing signal–usually because it is too far from your phone. There are often alerts for this as well–just keep in mind the possibility for alert fatigue if you are away from your phone often.

When you first apply the sensor, you might not have data for the first 30 minutes-2 hours. Finger sticks can be important at this time. During the first 24 hours after applying the sensor, the data may not be accurate. Always double-check with finger sticks periodically after applying your sensor. After the first 24 hours, double-check with finger sticks if the CGM reading doesn’t match how you feel, after compression, or if the reading changes rapidly. Remember that if you treat a low, you should rely on finger sticks to adjust treatment because of the lag in the CGM. This will help you avoid overtreating the low and feel better sooner!

Some models are also affected by your hydration and temperature. Dehydration can negatively affect accuracy, so be sure to stay hydrated! There are also medications and supplements [acetaminophen or high doses of vitamin C] that can cause inaccuracy in some CGMs. Check the manufacturer’s insert for guidance on your specific model.

Focus On The Trend, Not The Numbers

CGMs are best at showing the TREND in your blood sugar throughout the day. Focus on having a goal of keeping your blood sugar in a healthy range for a certain percentage of time. A healthy range will be different for everyone depending on age, type of diabetes, duration of diagnosis, health goals, prescribed medications etc. A general guideline is 70-140 mg/dL for those without diabetes and 80-180 mg/dL for people with diabetes. Obviously, pay attention to the extremes when looking at numbers in the day-to-day, but watching trends is more helpful for a picture of what your blood sugar is doing over time. Before wearing a CGM and monitoring your blood sugar, education on learning what a healthy blood sugar range is for you is key.

If a “health professional” tells you it’s not normal for blood sugars to “spike” please run the other way. Here’s why:

• A temporary rise in blood sugar is a natural response to eating a meal or snack, specifically one that contains carbohydrates. This is normal physiology.

• What is a “spike?” A spike is relative and there is no real definition of what it means. If it’s excessive and prolonged that’s when there could be a problem. Context like timing and the ability for the body to bring the blood sugar back to baseline matters more than the rise itself.

Supplies, Insurance, and All That Other Stuff

Just a few more tidbits to know about CGMs:

• They are durable and water-resistant, but not indestructible. Carry backup supplies like your finger stick meter and supplies, adhesives, overlays and alcohol wipes.

• CGMs may or may not be covered by your insurance. Check with them to learn what they do cover. Some CGM manufacturers offer assistance programs.

• If your sensor falls off, or just won’t adhere well, you’ll need to put on a new one. Call the manufacturer for a replacement if this happens. Also, replace early if you get repeated errors, or experience persistent inaccuracy.

To Sum It Up

CGMs are an amazing tool that can be incredibly helpful to those managing and living with diabetes. Always remember they are a TOOL, and each individual must determine the tools that work best for them. There is a learning curve associated with wearing a CGM, and it can feel overwhelming at times. Focus on the patterns, not perfection, and you may find that your CGM can be a great partner in your diabetes management plan.

Do you use a CGM? Love it? Hate it? Share your stories in the Your Diabetes Dietitian Facebook Group! Our community there is growing and we would love for you to join!