Episode 197: Continuous Glucose Monitoring
Written by William Zeng, MSIII, and Chris Kim, MSIII. University of Southern California.
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Will: Intro
Today we’re exploring Continuous Glucose Monitoring, or CGM. We’ll break down what CGM is, who benefits, how to access it, options available for our patients, the pros and cons, and a few final reflections on where this technology is heading. Chris, So what is CGM?
Chris:
Continuous glucose monitoring refers to the use of a small wearable sensor placed just under the skin to track glucose levels in real time throughout the day and night. These sensors measure glucose in the interstitial fluid and transmit readings to a receiver or smartphone at regular intervals, allowing for 24/7 glucose trend tracking.
Will:
CGM has been shown to improve glycemic control, increase “time in range,” and reduce hypoglycemia. Let’s review some evidence.
Chris:
A 2023 meta-analysis published in Diabetes Technology & Therapeutics reported a mean Hemoglobin A1c reduction of 0.43% across multiple trials.
Will:
In people with Type 1 diabetes, the IMPACT and DIAMOND studies showed sustained improvement in Hemoglobin A1c and hypoglycemia reduction over 6–12 months. CGM use in insulin-treated Type 2 diabetes patients also resulted in significant benefits, including reduced variability and fewer severe glucose excursions.
Chris:
Clinically and economically, CGMs help prevent long-term complications such as cardiovascular disease, nephropathy, and retinopathy. Chris, What patients specifically benefit the most from CGM?
Will:
CGMs are most commonly indicated for people with Type 1 diabetes and for those with Type 2 diabetes who are using intensive insulin regimens—typically defined as multiple daily injections or insulin pump therapy.
Chris:
And what are the qualifications in order to be covered by insurance?
Will:
In the United States, Medicare covers CGM as durable medical equipment for qualifying patients, and coverage requires a prescription, documentation of insulin use, and regular follow-up. Most major private insurers—including Blue Cross, Aetna, UnitedHealthcare, Cigna, and Kaiser—follow similar guidelines. Coverage is generally granted for patients with Type 1 diabetes or insulin-requiring Type 2 diabetes who monitor glucose at least four times daily or use an insulin pump.
Chris:
Some plans require demonstration of hypoglycemia unawareness or frequent glucose variability. For patients not on insulin, OTC CGMs may be an option, but coverage is typically not provided. That said, new FDA decisions are allowing over-the-counter access to CGMs like Abbott’s FreeStyle Libre and Dexcom’s Stelo, expanding availability for lifestyle or preventive purposes.
Will:
[There are a lot of products on the market. Which are the main products and how are they different?]
Chris:
The three main players in the CGM space are Dexcom, Abbott (FreeStyle Libre), and Senseonics (Eversense), each with unique offerings.
Let’s start with Dexcom. Dexcom G7 is a real-time CGM system approved for both Type 1 and Type 2 diabetes. It combines a sensor and transmitter into one compact wearable patch worn on the abdomen or upper arm for up to 10 days. It updates glucose readings every 5 minutes and connects directly to a smartphone or Apple Watch via Bluetooth. Dexcom also integrates with insulin pumps like Tandem’s t:slim and the Omnipod 5. Data can be shared with providers through Dexcom Clarity, which integrates into electronic medical records (EMRs) like Epic. OTC access is not yet available for DEXCOM G7, but a new non-prescription product called Dexcom Stelo is being rolled out in 2025, targeting non-insulin-using Type 2 patients. Dexcom Stelo will also offer 15-day wear, smartphone integration, and factory calibration. The estimated OTC cost for Dexcom Stelo is expected to be around $99 for a 15-day sensor, or about $198/month.
Will:
$200! Abbott FreeStyle Libre comes in several versions. The Libre 2 offers 14-day wear and requires users to scan the sensor with their smartphone or reader to retrieve a glucose value. It has optional real-time alarms for high and low readings and transmits data to LibreView, which can integrate with most EMRs. Libre 3 is a real-time CGM with 1-minute interval updates, Bluetooth transmission, and a slimmer profile. Libre sensors are widely used in primary care and available OTC for non-insulin users. Libre 2 sensors cost approximately $70–$85 for a 14-day sensor, while Libre 3 is slightly higher, around $85–$100 per sensor—totaling about $140–$200/month out of pocket without insurance.
Chris:
Senseonics Eversense E3 is the only implantable CGM on the market. It involves a minor in-office procedure to insert the sensor under the skin of the upper arm, which lasts up to 180 days (and a newer version, Eversense 365, lasts up to one year). A removable transmitter worn on top of the skin sends data every 5 minutes to a mobile app and vibrates for alerts. It requires 1–2 calibrations per day using a traditional fingerstick meter. It integrates with Eversense DMS software for physician monitoring. The total cost for Eversense depends on the insertion procedure and insurance, but cash pay for the full 6-month system is estimated at $2,400–$3,000, or about $400–$500/month including follow-up visits.
Will:
Additional lower-cost CGMs such as the Medtrum A6 TouchCare are available internationally and in select U.S. pilot programs. These devices offer 14-day wear, smartphone syncing, and daily calibration, but are not yet FDA-approved for wide use and lack full EMR integration.
Chris:
In terms of performance and value, Dexcom G7 offers the most advanced real-time feedback and integration, making it ideal for those on insulin pumps or needing tight control.
Will:
FreeStyle Libre offers the best affordability and convenience, especially for non-insulin users or those who prefer not to deal with constant alerts. Eversense offers a niche but compelling option for people who want to avoid frequent sensor changes. Chris, [Are there any downsides or risks that patients should be aware of before trying out CGM?]
Chris:
CGMs are generally safe and well-tolerated, but they do have limitations. Dexcom G7 has a known failure mode where sensors sometimes fail prematurely, often before the full 10-day duration. Some users have reported “signal loss” errors or random disconnections, especially when switching between phone models or operating systems. There are occasional reports of inaccurate highs or lows due to compression during sleep or dehydration. Though the G7 is factory-calibrated, abrupt changes in hydration or blood flow can affect its readings.
Will:
FreeStyle Libre systems, particularly Libre 2, require the user to scan the sensor to retrieve data unless alerts are enabled. These devices may be affected by vitamin C (ascorbic acid), which can falsely elevate glucose readings, and they do not currently allow for automated insulin delivery integration. Some Libre 2 users have noted adhesive-related rashes or spontaneous detachment. Libre 3, while more advanced, still may lose Bluetooth connection intermittently, particularly if the phone is out of range or the app is not running in the background.
Chris:
Senseonics Eversense carries procedural risks due to its implantable nature. Minor scarring or infection at the insertion site has been reported. The transmitter must be worn during waking hours to provide alerts, and users report anxiety over losing the transmitter since data logging is interrupted without it. Calibration is still required, which adds to daily tasks. Additionally, the sensor does not communicate with insulin pumps or closed-loop systems.
Will:
All CGMs can cause mild skin irritation from adhesive, particularly in users with sensitive skin. Alert fatigue is another consideration, as frequent low- or high-glucose warnings may cause stress or lead users to silence notifications entirely. Finally, relying solely on CGM without periodic fingerstick confirmation in symptomatic scenarios can be a risk, especially during rapid glucose changes.
Chris:
Conclusion
[***] Continuous glucose monitors have reshaped the way we manage diabetes, offering unprecedented insight into glucose trends, diet responses, and insulin timing. While CGMs are not flawless, the technology continues to evolve.
Will:
If your patient is on insulin or struggling with glucose variability, consider whether CGM is right for your patient. For those not using insulin, consider newer OTC options like FreeStyle Libre or Dexcom Stelo, which offer accessible entry points without the need for prescriptions. As AI integration, longer sensor life, and non-invasive monitoring enter the market, CGM will only become more useful.
Dr Arreaza: Personal experience with CGMs.
I do not have diabetes, but I have a strong family history of diabetes (including father, 2 grandmas, and about 15 uncles, aunts, and cousins.)
I wanted to try it so I could teach my patients about CGM. My first experience was with Freestyle Libre 2:
Pros: Painless placement, easy to use, scanning with phone was easier than fingersticks.
Cons: Required some assembling to be placed, mild discomfort at night, and nighttime alarms.
Dexcom G7:
Pros: No need for scanning, feels more stable in your arm
Cons: High readings (had to calibrate for a more accurate reading)
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