CGM User, Device Errors Pharmacists Should Understand | APhA 2025
Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES, discusses the various errors patients experience when using CGM devices.
There are several ways for continuous glucose monitoring (CGM) devices to function improperly, according to a session presented at the American Pharmacists Association 2025 Annual Meeting and Exposition.1 User errors, misinterpretation of data and other unforeseen events can lead to poor diabetes outcomes for those using CGM devices.
“There's a lot of education and counseling we can do to guide someone when they're putting [a CGM] on,” Diana Isaacs, PharmD, BCPS, BCACP, BC-ADM, CDCES, said in a presentation titled The Bucking Bronco: When CGM Goes Wild.
Ringing true to the title of her presentation, Isaacs went into depth on CGM errors and how these increasingly popular devices can truly “go wild.” Among those with diabetes using it to manage glucose levels or patients without diabetes simply looking to receive better health data, Isaacs discussed several instances where CGMs can malfunction. For pharmacists encouraging the use of CGMs among their patient population, it’s important they stay informed on these potential errors.
With consistent advancements in CGM technology, these errors are becoming less of an issue for diabetes patients and the pharmacists that counsel them. | image credit: Pixel-Shot / stock.adobe.com
READ MORE: CGM Could Help Management of Diabetic Ketoacidosis
CGM has existed since the late 20th century, when the FDA approved the first “professional” CGM device in 1999.2 Since then, several devices have been approved, with Dexcom and Libre devices being the most common among patients with diabetes.1 Despite significant advances in technology for the monitoring of blood glucose levels, user errors and device malfunctions have persisted.
“More than 80% of adults with diabetes using CGM reported at least 1 CGM disruption over the past year,” wrote Healio.3 “Device malfunction and insertion problems were the 2 most common reasons for CGM disruption.”
First, Isaacs discussed errors that involve the physical placement of CGMs. Aside from retrieving and portraying the correct data for patients, it’s important that they are wearing their device correctly. One issue many patients face is simply keeping their CGMs attached to wherever they are directed to place them on their bodies.
As one of the easier issues to resolve for CGM use, Isaacs mentioned that there is a plethora of products to assist in ensuring CGMs are worn properly. Of those products, Isaacs suggested the use of Mastisol liquid adhesive as an easy way to improve CGM placement.
Isaacs then discussed what usually occurs to yield data gaps in CGM and how this has become less of an issue due to the advancement of real-time CGM.
“If you don't scan at least every 8 hours, you will end up with some gaps in data. There would always be the person that maybe didn't know that, or only scanning once a day, and so we wouldn't have all of that data,” said Isaacs.1 “Fortunately now, all of the other ones, outside of the Libre 2 or 2-Plus system, are real time. That is much less of an issue. When we don't have sensor data, that is often because maybe it fell off and someone's not wearing it, or they didn't replace it right away.”
She also explained some more specific instances and patient events that could lead to gaps in data and device errors. Similar to errors portrayed when CGMs fall off the body, compression lows can occur and force the retrieval of false data.
“What a compression low is: let's say someone's wearing the sensor on their arm and they sleep on their arm. They're putting their whole body weight on their arm, and because it's measuring in that interstitial fluid, and all of that fluid is now squished up, it ends up reading falsely low,” she continued.1
Compression lows are a specific example of how pharmacists can counsel patients on their sleeping behaviors. While adherence to proper sleeping positions can be difficult to relay to patients, pharmacists should be aware of the various nuances of CGM use and the common errors that can occur.
Another way pharmacists can help patients avoid CGM errors is to make sure each patient using them understands the recommended time in range (TIR) settings.
“A patient changed their TIR to 70 to 130. Fortunately, our systems now default to 70 to 180, which was a change from a few years ago. Before that, it was like the wild west out there. So, they default to 70 to 180, but sometimes patients go in and they change it,” continued Isaacs.
With common occurrences of patients changing their target range settings, an opportunity is raised for pharmacists to educate on proper TIR settings for CGM devices. Another instance Isaacs has experienced among her patients is their urge to overcalibrate CGMs.
She explained that overcalibration of CGM devices can yield false data. “Unfortunately, [overcalibration] does not always make it better, because if you're putting garbage in, you may get garbage out,” said Isaacs. Other errors she’s seen included data not coming through on patient portals for CGMs, alarm fatigue causing patients to become nonadherent to data retrieval, as well as other medications interfering with CGM data.
However, with consistent advancements in CGM technology, these errors are becoming less of an issue for diabetes patients and the pharmacists that counsel them. But as long as these errors exist in some capacity, pharmacists should be knowledgeable on how to identify and address false data for CGM devices.
“It turns out there are several ways to mess up the data, including user error and data retrieval errors. I learned with any technology, there's always a way you can mess it up, and I think by getting more experience with it, you figure out those little nuances, and then they don't deter you,” concluded Isaacs.1
