Nov 27, 2023

Continuous glucose monitors, or CGMs, are an excellent way for people with diabetes or prediabetes to manage their condition. We tested some of the leading models to see which is best for you. Featured in this article 4 / 6 After my A1C test revealed prediabetes, I was determined to take steps to avoid the damaging effects of high blood sugar , including kidney disease, heart disease, and vision loss. I was unsure what to do, since I’m average weight, eat a healthy diet, and exercise regularly. I didn’t want to randomly experiment, then wait for my next A1C test to reveal whether my actions had made a difference. I needed to know how my behavior impacted my blood sugar. Luckily, this information is provided by a continuous glucose monitor (CGM), a quarter-sized disk worn on the back of the upper arm. CGMs are only approved by the US Food and Drug Administration for use by people with diabetes, and they require a prescription to purchase. While Medicare and most insurance programs won’t cover CGMs for people with prediabetes, some experts say CGMs are helpful for those at risk of diabetes. Eugene E. Wright, Jr. , a doctor and medical director of performance improvement at the South Piedmont Area Health Education Center in Charlotte, North Carolina, agrees. “CGMs are very useful for people with prediabetes, since diabetes complications can be reduced with early diagnosis and treatment,” he says. He adds that “research shows the benefits of early and aggressive treatment can last for 40-plus years.” Several popular CGMs aren’t covered in this review. I didn’t try the Eversense implanted device , but this may be a good option for those who need a sensor lasting six months. The Medtronic Guardian Connect and Eversense must be calibrated with daily fingerstick calibration, so I didn’t try those either. I also didn’t address factors important to users with specific needs (such as insulin pump compatibility, approval for use by children, etc.). While this is not an issue for many users, all CGMs measure “interstitial” glucose rather than blood glucose. Therefore, those using finger stick glucose to check CGM readings may find discrepancies in readings when blood glucose is rapidly changing. Photograph: MarkHatfield/Getty Images Key Features Ease of administration: All four CGMs were easily affixed to the back of my arm using a plunger device held against the skin. (I must admit that I’m not sure I could have done this on my own, at least the first few times. I engaged the help of my mechanical-engineering husband, who found administration straightforward.) All four sensors have a short monofilament that remains embedded in the skin. Event Tracking: All four allow tracking of food and exercise in the companion app and include a notes feature to track meal details and other important factors, like stress and sleep. Event tracking is critical for diagnosing what led to spikes, dips, or blood sugar variability, since individuals react to foods differently. Mahmood Kazemi , chief medical officer for Abbott’s diabetes care arm, says “there are no absolutes in terms of eating; what works for you may be different than what works for others.” He adds that “CGMs provide information needed to make educated decisions, since the impact of food choices can be different for each person.” Summary Reports: All four provide summary graphs that are useful for monitoring glucose range and trends, along with user-supplied notes. Daily reports that show actual blood glucose graphs, along with meals and notes about food, exercise, and stress, are very helpful for determining what behaviors and situations impact blood glucose. Water resistance: The FreeStyle Libre sensors are water resistant and work as long as they are not submerged more than 3 feet or kept underwater for over 30 minutes at a time. The Dexcom G7 is waterproof and may be submerged under 8 feet of water for up to 24 hours. I showered and worked out with all four CGMs without any issue. Support: All four systems provided user videos, phone support, and explanations about app functionality. Cost: Cash prices vary widely, so be sure to compare prices. I took advantage of substantial savings by checking prices and using online prescription discount services. Also, it’s worth remembering that the sensors have to be replaced periodically. Sensor prices are included below. Photograph: Abbott The Abbott FreeStyle Libre 2 offers the best bang for your buck. It was easy to provide my health care provider with access to my data through the app and simple to download reports to email. The sensor remained securely attached for the 14-day period. (In fact, it was a bit difficult to remove, and the adhesive circle remained so long that I wondered if my showering habits were subpar.) However, I didn’t like having to scan the sensor with my phone to get a reading, and I initially worried about missing important dips or peaks if I didn’t scan at the right time. I later learned that my concern was unfounded and that my graph would fully populate as long as I scanned my arm at least every eight hours. Wright prefers intermittent scanning because “it gives control to the user and because some users become overwhelmed with too much data,” he says. I’d buy this again if it was the lowest-price option. ($85 for two 14-day sensors.) Most Popular The Dexcom G-7 provided real-time continuous data without my having to scan the sensor, a huge plus for me. In addition, the Dexcom G-7 provided detailed reports that were easy to download and share, as well as quick weekend technical help. I found the thin, sticky protective cover incredibly difficult to place over the sensor, but I’m sure I’d do better the second time. Ten days of coverage is a bit disappointing compared to 14 days for the other three products. My sensor became loose on the ninth day, but there was no residue to scrub off. The Dexcom provides useful data, and I’d buy it if it was the lowest-price option. ($73 for one 10-day sensor.) Photograph: Abbott The FreeStyle Libre 3 had all the advantages of the Libre 2 (shareable data, great reports, helpful support), plus several additional features. I loved getting real-time continuous readings without having to scan the sensor with my phone. I also enjoyed the longer 33-foot Bluetooth range, which is 13 feet longer than the other three sensors. The sensor remained securely attached for the 14-day period—without a hard-to-scrub adhesive ring. When I order again, I’ll check for this sensor first. ($70 for one 14-day sensor, but I was able to obtain two 14-day sensors for $72 with a pharmacy-provided coupon, so check with your pharmacy.) Most Popular Best In-Depth Information: Nutrisense If you want a deep dive and have the time, interest, and extra funds, the Nutrisense program is your best bet. Two factors set Nutrisense apart from other programs: detailed learning and personalized nutritionist guidance. Nutrisense uses an Abbott FreeStyle Libre 14 day CGM. The sensor provides real-time continuous readings as long as the sensor is scanned every eight hours. As with the Libre 2, missing data is populated once the sensor is scanned. The 3-inch-diameter protective cover creates a larger footprint than the other CGMs, but it is easy to apply, stays secure for a 14-day period, and provides additional protection. Nutrisense doesn’t have an easy method for downloading reports and sharing data, other than exporting the raw data to a CSV file, but of course you can share data screenshots or review the phone app results with your health care provider. Photograph: Nutrisense A Word on Personalized Nutrition Blood sugar management can be complex, as many factors come into play (stress, sleep, food order, food choice, exercise, etc.). The Nutrisense educational program provides a thorough background of the factors that impact blood sugar, as well as suggested “experiments” to tease out the actual cause of dips, peaks, or variability. Keep in mind that these modules take time, so this is not a quick fix, but rather an approach for those who want a deeper understanding of blood sugar management. Until I tried Nutrisense, I didn’t have a health care professional regularly reviewing my CGM data, making suggestions to improve my blood glucose results, and answering my numerous questions. My case isn’t unique, according to Mahmood Kazemi, who says that the “majority of people living with diabetes see physicians with little or no experience with CGMs.” After three months of use, I found the addition of personalized nutritionist guidance to be invaluable. When asked, my nutritionist told me which of my metrics were acceptable and which needed improvement, and they provided suggestions for how to modify my behavior. With my goals in hand, it was easy to implement simple behavioral changes, like eating protein in the morning, adding eight deep breaths periodically while working, and taking a short walk after a heavy meal. The information I’ve received is worth the cost (especially early in my blood sugar management journey), but I can see how the amount of information could be overwhelming and difficult to digest over a short time period. Personalized nutrition can definitely help , but it’s not a cure-all, and it’s not useful for everyone . ($400 for two 14-day Nutrisense sensors and a month of education and personalized guidance. Lower costs are available for longer subscription periods: $299/month for the three-month plan, $250/month for the six-month plan, and so on.) I plan to integrate what I’ve learned from Nutrisense into my everyday life, then recheck my progress by using a CGM sensor every three months or so. I’m in good company with this approach. Wright says that he “finds it valuable for users to return to two weeks of CGM usage every few months to see if they are still on track for managing their blood sugar.” Then I’ll see what that dreaded A1C test says. Carol Milberger , Ph.D. is a retired Psychologist who writes about family, gratefulness, and resilience. Contributor