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.”
I selected four CGMs that are widely available, reasonably priced, easily applied, and use a smart phone as a transmitter: Abbott FreeStyle Libre 2, Abbott FreeStyle Libre 3, Dexcom G-7, and Nutrisense.
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.
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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.
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Photograph: Abbott
Best Value: Abbott FreeStyle Libre 2
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.)