Practical Tips for Optimizing Continuous Glucose Monitor Use

By Laura Hall, RN, CDE

As their accuracy increases and their ease of use is enhanced, continuous glucose monitors (CGMs) are becoming more common as a glucose self-monitoring tool for daily diabetes management.

Composed of a sensor inserted under the skin, the FDAapproved device constantly “reads” your blood glucose levels and transmits the information to a receiver where the levels are displayed, giving the user a window into the patterns of blood glucose highs and lows after eating different foods, engaging in physical activity and administering insulin.

There are now three types of sensors available in the United States. These sensors include: Medtronic Enlite/Guardian, Dexcom and Abbott Freestyle Libre. There are many similarities and some significant difference between these sensors (refer to reference chart on page 22 for details).

While the device provides users valuable information to help with their diabetes management, it’s important to understand how to optimize the performance of a CGM. Whether you are a savvy CGM user or considering CGM therapy for the first time, here are some common questions that patients frequently have about the proper use of CGMs.

How does the sensor work?

The sensor is inserted with a removable needle into subcutaneous (under the skin) tissue about 5 to 8 millimeters beneath the skin’s surface, where it measures interstitial glucose (blood sugar). Interstitial fluid is the fluid that surrounds the cells of your tissue below your skin.

Why is there a difference in sensor glucose versus blood glucose?

Glucose is first absorbed in the intestines and transported to the blood. Blood then carries glucose to to every cell in the body, including the interstitial tissue where the sensor is measuring glucose levels. Changes in glucose are first observed in the blood with a fingerstick and then observed at the interstitial tissue. There may or may not be a difference in sensor glucose and blood glucose measurements. It’s more common to observe a difference when glucose is rapidly changing, right after eating or during/after exercise, for example. However, sensor glucose trends should represent the change in glucose accurately, even if the blood glucose and sensor glucose do not match up perfectly at a given time.

What if I’m not getting accurate sensor data?

It can be a frustrating experience when sensor data and fingerstick blood glucose data aren’t consistent. There are a couple of steps to consider when this is a problem: stay hydrated or try wearing the CGM in a different site – either in the abdomen, upper thigh, arm or even just above the calf. Again, it is more likely that the sensor will not match the fingerstick blood glucose if glucose is rapidly changing.

The sensor will not stay on for the full seven or 10 days of wear. What can I do?

The tape that comes with the sensors is meant to last for seven to 10 days of wear, depending on the type of sensor you use. Skin types and activity level can affect how well the sensors remains adhered to the skin. Applying the sensor after a shower when the skin is totally clean and has minimal oil may help it adhere better. Also, make sure your skin is completely dry before applying the sensor. There are other tape options that can help reinforce the sensor. Some common products include: GrifGrips, Hypafix® and Skin Tac™. Skin Tac is like glue and can be applied to the sensor tape; then apply the sensor to the skin, as usual. Grif Grips and Hypafix are two of many excellent tape reinforcement options.

Can I reinsert my sensor if it falls off?

If part of the sensor that is inserted under the skin comes fully out, it can’t be reinserted. If the tape become loose or the sensor partially comes out, you can try to gently push the sensor back underneath the skin. It’s possible this will not work depending on how long the sensor has been hanging out of the subcutaneous tissue. It’s important to reinsert the sensor immediately if you notice it has partially come out. In this circumstance, make sure to initially monitor blood glucose more frequently with finger sticks in case the sensor was damaged and is unable to collect accurate data. If the data is not accurate, make sure to remove the sensor and insert a new sensor. Contact your sensor company to let them know there was a problem so the sensor can be replaced. Usually they will do this at no cost if you call within a reasonable time of when the problem/error occurred.

What do I do with the sensor when I shower?

Leave the sensor on. It’s important to make sure the sensor is well adhered to the skin prior to showering to prevent moisture from getting under the adhesive, which can cause it to loosen or become itchy. Avoid taking the receiver device in the shower unless the receiver is a waterproof pump. It’s best to leave the pumps or receivers in a safe space within 20 feet of the shower to avoid losing data connection.

Can I go swimming with my sensor?

Yes! All sensors are waterproof. The sensor may lose connection from the receiver device for a period of time depending on how long you spend in the water. The shorter the distance you are from the receiver and the shorter the duration in the water, the less likely your sensor data will be disconnected. If sensor data becomes disconnected from the receiver, usually once the sensor is back in range, it can reconnect automatically without a problem. If this doesn’t happen, make sure to call your sensor company to assist you with troubleshooting or send a new sensor, if needed.

What do I do when I need to go through airport security?

Most airports now have full-body scanners. Make sure to have TSA give you a pat-down if you’re wearing a sensor. Some of the sensors can go through the x-ray machine. Check with the device manufacturer.

What do I need to do when I have an MRI, CAT scan or X-ray?

The sensor needs to be removed for a CT or MRI scan. If the area of the body undergoing an X-ray is located where the sensor is worn, it needs to be removed. If the sensor can be protected from X-rays with a lead covering, it can be worn during the procedure.

Can I wear the sensor during other medical procedures?

Discuss this with the medical team performing the procedure. If this is a procedure that requires anesthesia (being put to sleep for a period of time), you should not need to take the sensor off so you can resume using sensor data after the procedure. Ask your medical team members if they want to be alerted to the continuous glucose data during the procedure. Make sure they are aware of the location of the sensor on your body so they can avoid dislodging it. During procedures in which you will be awake, such as mole removal, root canals, and so forth, make sure the team knows you have a device that has an alarm.

If I have a headache, can I take acetaminophen (Tylenol®)?

Most drugs do not interact with the sensor data. Unfortunately, Tylenol may cause a false sensor glucose “high” with the Dexcom receiver. If Tylenol needs to be used while wearing the Dexcom, close the receiver app on the phone and disregard sensor data for eight to 10 hours until the Tylenol has cleared out of your system.

If my back hurts, can I take aspirin?

Aspirin does not interact with any sensor data.

Can I use a sensor if it is 30 days post expiration date? Ninety days post expiration date?

Technically the sensors should not be worn after the expiration date. This is because the data may not be accurate. It won’t hurt your body, it just may not be helpful. Given how expensive sensors can be, it is understandable that you may want to wear it beyond the expiration date. If you choose to wear a sensor beyond the expiration date, be aware that the data may not be accurate. In this circumstance, it’s very important that treatment decisions be made based off fingersticks, not just sensor data alone. If the data turns out to be consistently and significantly inaccurate, the sensor should be removed.

I don’t want to do fingersticks. Can a sensor replace them?

The Libre is the only factory-calibrated sensor that doesn’t require additional fingersticks for calibrations or treatment decisions. Some people experience remarkably accurate sensor data with minimal fingersticks with Dexcom and Medtronic sensors as well. Discuss with your diabetes care team whether it is safe for you to bypass fingersticks. Always use a fingerstick with clean hands if you have any reason to believe the sensor glucose is not accurate. And don’t make treatment decisions based on symptoms of low or high glucose, especially if how you feel is not consistent with the sensor glucose data.