Continuous Glucose Monitors : A Comprehensive Guide

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Brief history of glucose monitoring

Blood glucose is an important monitoring parameter when it comes to diabetes management. Attempts to quantify glucose in the urine date back to the mid-1800s, but the most important development in the commercialization of urine glucose testing was made in 1908 by Benedict, who developed a copper reagent for urine glucose.

The cumbersome methodology involved in glucose monitoring became more convenient in 1945 with the development of Clinitest, and in 1965 Ames developed the first blood glucose test strip, the Dextrostix, based on a glucose oxidase reaction.

By the mid-1970s, the concept of patients using blood glucose data at home was contemplated, and by 1980, the Dextrometer was launched. This meter used the Dextrostix along with a digital display. During the 1980s, meters and strips requiring less blood became available at a cheaper price. Self-monitoring of blood glucose (SMBG) became the standard of care, especially for patients with type 1 diabetes.

Through the late 1980s, 1990s, and early 2000s, SMBG technology continued to improve. The blood removal step was eliminated, smaller amounts of blood were required, electrochemical strips were developed, wider ranges of hematocrit were permitted, and new enzymatic tests were used.

The evolution of home glucose monitoring was further revolutionized with the introduction of continuous glucose monitoring (CGM). In 1999, the U.S. FDA approved the first “professional” CGM. The first “real-time” CGM was the Glucowatch Biographer, but it did not succeed.

 In 2004, Medtronic introduced the Guardian REAL-Time CGM system, which could notify users of potentially dangerous hyperglycemia or hypoglycemia, and by 2006, the same company released the first integrated pump and sensor.

Dexcom and FreeStyle Navigator are followers of the Guardian, and all of them required blood glucose confirmation for treatment decisions to be made.

Modern times require modern solutions, so G4 Platinum in 2012, followed by G5 Mobile in 2015 allowed data to be transmitted to the user’s cellphone. The medtronic Minimed 630G integrated with thee Enlite sensor by Medtronic was the first insulin pump with “threshold suspends” for hypoglycemia. The threshold suspend featured allowed the pump to halt insulin infusion when anticipated blood glucose based on CGM readings was anticipated to be close to the limits hypoglycemia.

Medtronic’s first hybrid closed-loop device was available in 2017 using the Guardian Sensor 3. Abbott introduced the FreeStyle Libre Pro in 2016. This professional CGM was the first that required no fingerstick testing during wear. The professional CGM however could not be used for immediate treatment decisions by the patient. The data had to be downloaded at a later date for interpretation by a diabetes resource provider.

The FreeStyle Libre, for direct use by patients, became available in the United States in late 2017, allowing patients to read the data themselves. In less than 20 years, CGM has revolutionized the way diabetes is managed, especially type 1 diabetes.

Importance of glucose monitoring

Living with diabetes 24/7 is challenging. Understanding the value of continuous blood glucose monitoring can help patients with diabetes take charge of their self-management and play an active role in decision-making regarding their diabetes treatment.

Understanding their blood glucose monitoring data can motivate them to make healthier choices and build their self-confidence.

Advantages of Continuous Glucose Monitors (CGMs)

The advantages of CGM are many:

  • It allows you to track your blood glucose levels any time of the day or night, understand what your blood sugar levels are doing at times when you don’t normally test, like when you are sleeping
  • Share your data with your diabetes team remotely
  • Get insight into how factors from your daily life including food, exercise, stress, medications, hormones, and illness affect you.
  • Moreover, program alarms to alert you if your blood sugar is too high or too low, take action sooner to prevent dangerous hypos and tailor your insulin doses more carefully based on a better understanding of your blood sugar levels. These things can help overcome your fear of sudden hypos and have more confidence in your decision-making ability when administering insulin.
  • Also, it reduces the number of finger-prick tests you need to do.

In the long term, analyzing your data with your diabetes team can help you come up with personalized strategies for your care and improve your HbA1c level over time through better day-to-day blood glucose management.

Glucose-monitoring technology has been established and refined since the 1980s, providing essential benefits to individuals with diabetes from both a clinical and financial perspective—particularly if used to its fullest potential. By knowing their glucose levels, people can adjust insulin doses, diet, or other lifestyle components to keep glucose levels within recommended ranges. Expert organizations propose specific glucose targets, which usually include A1C, self-monitored blood glucose (SMBG), and interstitial glucose measurements. While each authority may use slightly different targets, most advise tailoring them to each individual’s risk of hypoglycemia, medication regimen, comorbidities, and other factors that may influence long-term outcomes. Recent guidelines from the American Diabetes Association (ADA) also emphasize additional markers for evaluating overall glucose control, such as time in range (TIR)—the percentage of time glucose levels remain between 70–180 mg/dL—and the Glucose Management Indicator (GMI), an estimate of A1C derived from 14-day continuous glucose monitoring (CGM) data.

Trends in Glucose Monitoring

Glucose monitoring technology is evolving rapidly. A broad overview of available devices can be found in many published reviews, but below are several emerging trends in monitoring that merit closer attention:

  1. Continuous Glucose Monitoring (CGM):
    Evidence supporting CGM’s clinical benefits has grown substantially, leading to broader use. Because CGM gathers data continuously, it allows more precise, data-driven adjustments in both insulin dosing and lifestyle choices compared to single-point measurements from SMBG. Recent developments include simpler data collection methods and the exploration of noninvasive monitoring tools.
  2. Closed-Loop Control (CLC):
    Sometimes referred to as a “bionic” or “artificial” pancreas, CLC integrates CGM data with automatically controlled insulin delivery. Early versions of these systems are already available, marking significant progress toward fully automated insulin regulation.
  3. Mobile Technology and Decision Support:
    Glucose-monitoring systems increasingly connect to smartphones and other mobile devices, supporting patient self-care, improving data sharing, and facilitating more immediate clinical interventions.
  4. Alternate Glucose Control Markers:
    Researchers continue exploring other laboratory markers beyond glucose that might help track glycemic control; although clinical use of these markers remains under evaluation, they could potentially complement or refine standard glucose measures.

CGMs typically measure interstitial glucose around the clock, with readings updated every few minutes. A typical setup includes:

  • A display device (often a smartphone),
  • A sensor placed beneath the skin,
  • A transmitter sending data to the display.

Initially, CGMs were only cleared as supplemental devices, meaning individuals still needed fingerstick glucose tests to confirm readings and guide insulin therapy. Over time, improvements in sensor accuracy have allowed certain CGMs to be used with fewer or no calibrations, though readings in the hypoglycemic range remain less precise and still require attention.

By revealing high or low glucose values, predicting imminent lows, and displaying wide variability, CGMs help both patients and providers make more precise decisions about therapy and lifestyle. Many systems have 24-hour technical support. Efforts are underway to integrate CGMs fully with automated insulin delivery systems, advancing toward a true artificial pancreas.

CGMs can be:

  • Professional CGM: Owned by the clinic, sometimes used in a “blinded” mode.
  • Personal CGM: Patient-owned, providing live glucose data on a continual basis.

Professional CGM

Professional CGM is managed by healthcare providers, who lend the sensor and monitor to patients for a fixed period. Patients may not see their results in real time; instead, the data are downloaded at a later point. This setup reveals glucose trends in everyday life without the patient making reactive changes during the monitoring period. Professional CGM can be useful for identifying hidden issues such as nocturnal hypoglycemia, dawn phenomenon, and post-meal hyperglycemia. Many insurance plans reimburse professional CGM, and specialists who interpret these data may be eligible for monthly billing.

Several systems can be run either as professional or personal CGM, depending on whether real-time visibility is turned on or off. Improvements in professional CGM over the years have included enhanced accuracy and better patient comfort. In some studies, professional CGM led to modest but meaningful reductions in A1C and slight increases in time spent in a healthy glucose range.

FreeStyle Libre Pro

The FreeStyle Libre Pro uses the same sensor as the consumer version but is managed by a healthcare team. It’s factory-calibrated (no daily fingerstick checks for calibration) and logs data continuously for up to 14 days, storing glucose values every 15 minutes. A single clinic reader activates and scans multiple patient sensors, making large-scale professional CGM simple. Reports analyze daily patterns, risk of hypoglycemia, glucose variability, and overall control. Its accuracy is generally strong, with somewhat weaker performance during day one of use and at lower glucose levels.

Dexcom Professional

The Dexcom G6 Pro can run in a blinded or unblinded mode. It collects interstitial glucose every 5 minutes and has a 10-day sensor lifespan. When used in a blinded format, the patient does not see the data in real time; once the sensor is removed, a healthcare professional reviews the recorded glucose data. Like other Dexcom devices, it requires no routine calibration.

Retrospective Data Analysis
Regardless of brand or model, CGMs allow a retrospective examination of glucose data. Patients may be asked to keep records of food, exercise, and medications to facilitate interpretation. Clinicians generally pay close attention to patterns overnight, before meals, and after meals, because issues in each of these intervals might call for different treatment changes.


Ambulatory Glucose Profile (AGP)

The AGP is a standardized, user-friendly report consolidating CGM data into visual summaries. It usually includes:

  1. Statistical Summaries: Average glucose, time above/below target, time in range, and fluctuations.
  2. Modal Day View: All days’ data compiled into a single 24-hour visualization to highlight repeating patterns.
  3. Daily View: Detailed, day-by-day readings for deeper exploration of anomalies.

This approach helps simplify what can otherwise be lengthy or complex data sets, making it easier to identify therapy adjustments quickly.

Composite Metrics
Time in range (TIR) has gained traction as a core CGM metric, but it doesn’t always capture the full clinical picture. Various composite measures aim to weigh extreme highs or lows more heavily, as these pose greater risk. For example, the Glycemia Risk Index (GRI) assigns extra weight to very high or very low glucose values, aligning with many clinicians’ assessments.


Personal CGM: Real-Time (RT-CGM) or Intermittently Scanned (IS-CGM)

Personal CGMs display glucose readings in near-real time or let the user scan a sensor to get current readings. RT-CGMs can proactively alert users to rising or falling glucose or to actual threshold-crossing events. IS-CGM typically omits continuous, automatic alerts unless the user chooses to scan. In some research, RT-CGM has slightly outperformed IS-CGM for reducing episodes of hypoglycemia and increasing time spent within target, particularly among people with type 1 diabetes.

Newer “no-calibration” devices permit direct treatment decisions based on sensor readings. Still, all continuous monitors must manage a trade-off between catching all potential lows (high sensitivity) and avoiding false alarms (high specificity). Overall, CGMs can help reduce glycemic variability and may benefit people with both type 1 and type 2 diabetes.


Evidence in Type 1 Diabetes

Studies With Both Pump and Injection Users
Many studies demonstrate that continuous, consistent use of RT-CGM lowers A1C, reduces time in hypoglycemia, and improves daily glucose stability. Lack of benefit often occurs in studies where patient adherence is poor.

Studies With Insulin Pump Therapy
A large trial comparing sensor-augmented pump therapy to multiple daily injections reported significantly better A1C results in the pump group, without increased hypoglycemia risk.

Studies With Multiple Daily Injections
Multiple studies show RT-CGM or IS-CGM improves A1C, reduces time below target, and lessens glucose variability compared to standard SMBG alone.

Patients With Hypoglycemia Unawareness
Research targeting people prone to severe low blood sugars reveals significant reductions in dangerous lows when CGM is used, though some findings vary based on device adherence and other study conditions.

Patient-Reported Outcomes
Improvements often show up in areas like worry over low blood sugar and overall treatment satisfaction, even when generic quality-of-life scales do not change dramatically.


Evidence in Type 2 Diabetes

In those with type 2 diabetes—ranging from non-insulin users to those on intensive regimens—CGM can encourage lifestyle improvements and better glucose regulation, sometimes by small but meaningful margins. Some trials used brief “on-off” CGM periods every few months to help reinforce education and encourage consistent behavior changes.

Real-world data strongly suggest that CGM use among people with type 2 diabetes correlates with fewer hospitalizations, improved A1C, and reduced glucose variability. Sustaining CGM over longer periods appears integral to maintaining these benefits.


Recommendations

Appropriate individuals must understand CGM’s limitations and become competent with its use, which can still require occasional fingersticks. Ongoing education in insulin dosing and carb counting is highly recommended. Several specialty groups advise that adults with type 1 diabetes or with frequent hypoglycemia benefit greatly from near-daily CGM usage. Meanwhile, shorter-term CGM use can be useful for many with type 2 diabetes who are motivated to understand and improve their glucose patterns.

Understanding Continuous Glucose Monitors

What is a CGM?

Continuous glucose monitors (CGMs) constantly track your blood glucose levels, providing real-time updates via a device connected to your body.

Over the years, CGMs have gained popularity and become more precise, making them a reliable treatment choice for individuals with diabetes. A continuous glucose monitor (CGM) allows users to see if their glucose levels are trending high or low in real-time, enabling them to take preventive action against hypoglycemia and hyperglycemia. Real-time CGM monitoring has significantly improved outcomes for people with diabetes who, without a CGM, might have faced potentially life-threatening complications.

How does it work?

A CGM operates by using a small sensor inserted beneath your skin, typically on your abdomen or arm. This sensor measures your interstitial glucose levels, which refers to the glucose present in the fluid between cells. The sensor evaluates glucose levels every few minutes, and a transmitter wirelessly relays this information to a monitoring device.

This monitor could be integrated into an insulin pump or a separate device that you can carry in your pocket or bag. Some CGMs can also transmit data directly to a smartphone or tablet.

CGMs are constantly monitoring glucose levels during various activities, such as showering, working, exercising, or sleeping. Many CGMs come with special features that utilize data from your glucose readings, such as alarms that trigger when your glucose level is too high or too low. You can also record information about meals, physical activities, and medications within a CGM device.

Along with your glucose levels, you can transfer data to a computer or smart phone to analyze glucose trends. This is certainly helpful for your healthcare provider in assessing your diabetes control. Furthermore, certain models can instantly transmit information to a secondary person’s smartphone, like a parent, partner, or caregiver. For instance, if a child’s glucose level drops dangerously low during the night, the CGM can be configured to alert a parent in a nearby room.

The Dexcom series, Medtronic Guardian and Freestyle Libre sensors are approved for making treatment decisions. This means you can adjust your diabetes care plan based solely on CGM results. With legacy models from these CGM manufacturers, you had to first verify a CGM reading with a finger-stick blood glucose test before administering insulin or treating hypoglycemia.

Types of CGMs

  • Dexcom G6 and Dexcom G7
  • Freestyle libre, Freestyle libre 2, Freestyle libre 3 and Freestyle Libre 3 plus
  • Eversense senseonics
  • Medtronic guardian sensor 3, and guardian sensor 4.

Many types of CGMs have evolved over the years, and there have been exciting improvements in the accuracy, reliability, and ease of use of these devices. Indeed, there are some specific differences between the two main types of CGMs, real-time and intermittently scanned. However, each has its unique feature that can impact its usefulness and acceptability in specific groups of patients.

Dexcom G6 : The Dexcom G6 CGM system sends real-time glucose readings automatically to a compatible smart device or Dexcom receiver. Fingersticks and scanning are not needed and even more importantly, it features a 10-day sensor easy to use.

Dexcom G7 : Delivers real-time glucose numbers to a smartphone or a smartwatch. It also does not require fingersticks. The advantage of the G7 over the G6 includes it’s less bulky profile (60% smaller) and greater accuracy.

Freestyle libre 3 : The Freestyle Libre 3 is designed to be worn on the back of the upper arm and constantly monitors glucose levels in the interstitial fluid of the body, both day and night. The sensor refreshes glucose readings as often as every 5 minutes and directly transmits the data to a compatible smartphone. With a wear time of up to 14 days, the device is water-resistant, ensuring its functionality remains intact while swimming, showering, or exercising.

Eversense senseonics Although all CGM systems utilize sensors that are inserted through the skin and have a lifespan of 7-14 days, the Eversense sensor is uniquely implanted beneath the skin for long term glucose monitoring. With the Eversense CGM system lasting up to 6 months, it effectively eliminates the inconvenience and discomfort associated with frequent sensor insertions. Adoption of this sensor has however been limited for various reasons. The need for it’s insertion in a physician office may is a limitation. In addition, the need for fingerstick calibrations makes it less appealing to patients compared to the Dexcom G7 and Freestyle libre 3.

Medtronic guardian sensor 3 : This sensor has a Mean absolute relative difference (MARD) of 8.7%.

Medtronic guardian sensor 4 : The newest sensor from medtronic is the guardian sensor 4. It requires no finger sticks and also checks your blood glucose every five minutes. Medtronic’s state of the art hybrid closed loop insulin pump, the MiniMed™ 780G system, integrates with the guardian sensor 4 to proactively predict insulin requirements, fine-tune insulin delivery, and automatically correct high glucose levels while safeguarding against lows.

DeviceCalibration RequiredFingersticks Required Before TreatmentReal-Time AlertsSensor Life (days)Warm-Up (hrs)Remove for MRI/CT/DiathermyAcetaminophen InterferenceCompatible with insulin pumps
Dexcom G5Yes (Y)No (N)Yes (Y)72Yes (Y)Yes (Y)Yes (Y)
Dexcom G6No (N)No (N)Yes (Y)102Yes (Y)No (N)Yes (Y)
Dexcom G7No (N)No (N)Yes (Y)100.5Yes (Y)No (N)Yes (Y)
Medtronic Guardian 3Yes (Y)Yes (Y)Yes (Y)72Yes (Y)Yes (Y)Yes (Y)
FreeStyle Libre 14-DayNo (N)No (N)No (N)141Yes (Y)No (N)No (N)
FreeStyle Libre 2No (N)No (N)Yes (Y)141Yes (Y)No (N)No (N)
FreeStyle Libre 3No (N)No (N)Yes (Y)141Yes (Y)No (N)No (N)
Freestyle libre 3 plusNo (N)No (N)Yes (Y)151Yes (Y)No (N)Yes (Y)
Eversense (Implanted)Yes (Y)No (N)Yes (Y)180N/AYes (Y)NoNo (N)
  • Calibration Required: Indicates whether regular fingerstick calibration is necessary (Y = yes, N = no).
  • Fingersticks Required Before Treatment: Shows if confirmatory blood glucose checks are needed prior to treating based on CGM data.
  • Real-Time Alerts: Whether the device can alert the user automatically to rising/falling glucose levels.
  • Sensor Life: Approximate number of days the sensor can be worn.
  • Warm-Up Period: Time the sensor needs before providing readings.
  • Removal for Imaging: Sensors typically need to be removed for MRI, CT scans, or certain diathermy treatments.
  • Acetaminophen Interference: Some CGMs may show falsely elevated readings when users take acetaminophen (also known as paracetamol).

Accuracy and reliability

Most CGM systems assess glucose in the subcutaneous interstitial fluid, using the glucose oxidase approach. This provides minimal discomfort to patients and allows CGM usage at home.

Recent developments in CGM technology has improved their MARDs, making them very reliable and accurate enough to make treatment decisions.

Who can benefit from CGMs?

People with diabetes

Individuals with type 1 and type 2 diabetes on multiple daily doses of insulin (MDI) should utilize a CGM. The primary reasons for this preference among those with diabetes include increased feelings of safety, improved glucose management, reduced discomfort from finger sticks. Furthermore, the ability to connect with an insulin pump to create a closed-loop system (or artificial pancreas) helps to further optimize diabetes control.

Athletes and fitness enthusiasts

Keeping track of glucose levels can improve the quality of life for a fitness enthusiast. Having a positive impact on performance and energy levels is just one of the many benefits of glucose monitoring through a CGM.

For instance, endurance athletes may be training for long periods, so If they don’t fuel appropriately before and during training, they can risk low blood sugar – hypoglycemia. Hypoglycemia can lead to feeling a loss of energy, decreased performance, and even fainting.

Using the CGM, an athlete can monitor for dips in glucose or decreases in glucose during training and plan their fueling strategy accordingly. The CGM allows them to measure glucose during training without stopping and taking measurements. In addition, there is evidence that CGM devices are accurate during intense training. Although there is limited research, there is evidence that CGM can help increase performance and recovery.

Individuals with a history of hypoglycemia

A continued decline in glucose eventually leads to neurologic dysfunction, widespread electroencephalogram (EEG) changes, cognitive dysfunction, and severe neuroglycopenia. Counterregulatory abnormalities such as absent suppression of insulin secretion blunted or absent glucagon response, and blunted adrenaline response further exacerbate the hypoglycemic condition in Type 1 and advanced Type 2 diabetes. Patients who experience frequent episodes of hypoglycemia often develop these abnormalities and lose their ability to detect hypoglycemia; this is referred to as “hypoglycemia unawareness” and it perpetrates a vicious cycle of recurrent hypoglycemia. CGM can play a significant role in preventing hypoglycemia. Unlike traditional blood glucose monitoring, which looks at only a few points in time, CGM provides comprehensive data that track glucose levels 24 hours a day. This information allows patients to optimize their glycemic control and thus minimize the frequency and severity of hypoglycemic events.

Choosing a CGM

Factors to consider when choosing a CGM

Insurance coverage: Consult your insurance provider to determine coverage details, as some may restrict coverage to specific models

Cost: CGMs differ in price, so consider the cost of sensors since they will constitute the majority of the expense over time.

Ease of use: The usability of CGMs varies, with some requiring intermittent scanning or calibrations, making them less applicable to all patients with diabetes mellitus.

Comparison of popular CGMs in 2025

FeaturesDexcom G7Guardian Sensor 4Freestyle Libre 3Eversense E3
ManufacturerDexcomMedtronicAbottSenseonics
Mean Absolute Relative Difference8.20%9.60%7.90%8.50%
Approved SitesBack of upper arms or upper buttocksBack of upper arms or upper buttocksBack of upper armsBack of upper arms
Warm up30 minutes2 hours60 minute warm up24 hours
Duration of wear10 days7 days14 days180 days
Insulin pump integrationTandem T Slim X2 (pending as of March 2023)Minimed 780GNot yetNot yet
Smartphone appYesYesYes (not compatible with all models)Yes
Sharing of dataYes (Dexcom follow)Yes (Carelink Connect)Yes (libre link app)Yes
Water ResistanceYesYesYesYes

Important Features of CGMS by brand

Guardian Connect (Medtronic)

Key Features

  • Components: Uses the Guardian Sensor 3, the Guardian Connect transmitter, and the Guardian Connect mobile app.
  • Data Transmission: Sends glucose data via Bluetooth every 5 minutes to a compatible smart device. Initially, this system was only available on iOS platforms, but additional device compatibility may expand over time.
  • Data Display and Sharing: A dedicated receiver is not included. Instead, data appear on the Guardian Connect app for smartphones. Users can also use CareLink (both personal and professional versions) for broader data review.
  • Alerts and Communication: Allows remote data sharing and can send SMS messages or notifications to caregivers or family members—particularly useful during episodes of low glucose.
  • Adjunctive Use Only: The FDA presently approves Guardian Connect as an adjunctive system, meaning it requires at least two daily fingerstick calibrations to confirm sensor readings before making treatment decisions.

Additional Considerations

  • People seeking direct insulin dosing from CGM data (non-adjunctive use) would still need another system or additional fingersticks to confirm glucose levels.
  • The Guardian Sensor 3 may be integrated with some Medtronic insulin pump features, but Guardian Connect specifically focuses on smartphone-based data displays rather than a dedicated receiver.

Dexcom G6

Key Features

  • Sensor Design: Uses a subcutaneous wire-based glucose oxidase sensor to measure interstitial glucose levels.
  • Wireless Data: Transmits readings to either a dedicated receiver or directly to a smartphone, providing near–real-time data updates approximately every 5 minutes.
  • Sensor Life: Each sensor can be worn for up to 10 days.
  • Calibration: Factory-calibrated—routine calibrations with fingersticks are not required.
  • Medication Interference: Includes built-in acetaminophen-blocking technology, reducing the risk of false-high readings that older models sometimes encountered.
  • Smartphone Integration: Users can access a Dexcom G6 app to log exercise, view trends, and receive customizable alarms or reminders.
  • Data Management: Dexcom CLARITY software compiles and analyzes glucose patterns, creating user-friendly reports.
  • Remote Monitoring: Through the Dexcom SHARE function, up to 10 people (such as caregivers, friends, or family) can view a user’s glucose data.

Additional Considerations

  • Widely integrated with certain automated insulin-delivery systems (AID).
  • Does not require confirmatory fingersticks unless sensor readings appear inconsistent with symptoms.

Dexcom G7

Key Features

  • Reduced Size: About 60% smaller than the G6 (similar to stacking three quarters); the entire sensor and transmitter are combined into one disposable unit.
  • Faster Warm-Up: Warm-up time is approximately 30 minutes (compared to 2 hours for G6), with a 12-hour grace period at the end of the sensor’s wear time to simplify sensor changes.
  • Reported Accuracy: Overall mean absolute relative difference (MARD) is roughly 8–9%, depending on sensor location (abdomen vs. arm). Accuracy tends to be slightly lower when glucose is dropping or rising quickly, and on the first day of wear.
  • No Manual Calibration: Continues Dexcom’s practice of factory-calibrated sensors.
  • Smartphone Integration: Similar to the G6, but with updated app features that reflect the G7’s new warm-up and design.
  • Disposable Design: Entirely disposable after the wear period, streamlining the user’s workflow.

Additional Considerations

  • As with many CGMs, day-one readings and rapid glucose excursions can slightly reduce accuracy.
  • The G7’s smaller form factor is appealing for users seeking a less obtrusive device.

FreeStyle Libre 14 Day (Abbott)

Key Features

  • Wired Enzyme™ Technology: The sensor’s enzyme and mediator are co-immobilized, enabling factory calibration—thus eliminating the daily need for fingerstick calibrations under most conditions.
  • Sensor Life: FDA-approved for up to 14 consecutive days of wear.
  • Data Capture: Records glucose every minute and saves an average every 15 minutes.
  • Alerts and Displays: Unlike typical real-time CGMs, the Libre 14 Day does not automatically alert users of high or low glucose. Instead, a handheld reader or smartphone app (FreeStyle LibreLink) must “scan” the sensor to retrieve updated data.
  • Fingerstick Confirmation: Recommended if glucose readings do not match how the user feels or during times of rapid changes in glucose. A built-in blood glucose meter in the reader is available for such checks.
  • Acetaminophen Interference: Abbott’s design has minimized interference with acetaminophen, though potential interference from other substances—like ascorbic acid—may still occur.
  • Age and Condition Restrictions: Not officially approved for individuals younger than 18, pregnant users, or those on hemodialysis.

Why Some Users Prefer It

  • Often described as convenient and low-maintenance compared to real-time CGMs.
  • Scanning the device can feel simpler to users who do not want frequent alarms or continuous data uploads.
  • The cloud-based LibreView platform and desktop software make it straightforward for both users and clinicians to review patterns and trends.

FreeStyle Libre 2 (Abbott)

Key Features

  • Optional Real-Time Alerts: Adds a built-in alarm system that can notify wearers if glucose rises too high or drops too low, addressing a common limitation of the original Libre 14 Day.
  • Sensor Memory: Retains 8 hours of data. If the sensor is not scanned within that window, older readings are overwritten.
  • Accuracy Improvements: Features refinements that improve accuracy slightly over the previous generation, though scanning remains essential to see the actual glucose value.
  • Age Indication: Approved for users as young as 4 years old, broadening its applicability compared to the 14-day system’s original label.

Additional Considerations

  • Like the original Libre 14 Day, actual glucose numbers remain hidden until scanned, but high/low glucose alarms provide more real-time awareness.
  • Requires confirmatory fingerstick only if sensor readings appear incompatible with physical symptoms.

FreeStyle Libre 3 (Abbott)

Key Features

  • Smaller Profile: Approximately the size of two stacked pennies, making it one of the most compact CGMs currently available.
  • Continuous Data Transmission: Differing from earlier Libre models, the Libre 3 broadcasts glucose readings continuously and can update the user’s smartphone without scanning.
  • Extended Bluetooth Range: Improved from 20 ft. to about 33 ft., helping to keep a reliable connection for real-time data.
  • Accuracy: Slightly improved relative to Libre 2, with a reported overall MARD around 9% in adults and roughly 10% in children.
  • Smartphone Dependence: Requires a compatible smartphone for data display and alarms—no dedicated reader is available.

Key Benefits

  • Combines the ease of the Libre systems with real-time transmissions and alarms.
  • Maintains a small sensor size to enhance user comfort and discretion.

Eversense (Senseonics)

Key Features

  • Implantable Sensor: Inserted under the skin, where it can remain for up to 90 or 180 days (depending on the model). A removable transmitter sits on top of the skin and sends data to a smartphone app (Eversense NOW).
  • Fluorescent Measurement: Uses a light-based detection system rather than the enzyme-based approaches commonly seen with other CGMs.
  • Wear Duration: The original version lasts about 90 days, whereas Eversense XL can last up to 180 days. This extended interval is appealing to those who prefer fewer sensor changes.
  • Accuracy: Studies have reported mean absolute relative differences (MARD) between 9% and 11%, generally comparable to other CGMs.
  • Medication Interference: Avoids major problems with acetaminophen or vitamin C that can affect enzyme-based sensors, though certain drugs (like tetracycline) may affect readings.

Why Some Users Choose Eversense

  • Can be beneficial for users with needle phobias, skin adhesion issues, or those who lead active lifestyles that make external sensors cumbersome.
  • Offers consistent accuracy over extended periods, reducing the need to replace sensors every week or two.
  • The on-body transmitter can be removed if needed (for short intervals), such as during contact sports or other activities.

CGMs and Time in Range

Time in Range (TIR) is more than just another diabetes metric; it is a tool that can be used to improve communication with your healthcare providers and empower you both in the doctor’s office and beyond.

Conversations about A1C with your healthcare providers can often feel one-sided. It can be difficult to discuss A1C results that you are seeing for the first time, leaving your healthcare team to do most of the talking. Because A1C is only an average measure of your glucose management over a period of three months, it cannot provide information about how your day-to-day actions affect your glucose. In contrast, Time in Range fosters a more dynamic conversation because people with diabetes can discuss the TIR data they live with day-to-day.

TIR is measured using a continuous glucose monitor), which measures glucose levels automatically every five minutes. These numbers can be graphed to show the percentage of time spent within a healthy glucose range between 70-180mg/dL (or, Time in Range), giving the user much more information about their glucose patterns each day.

A person with diabetes knows the most about their daily diabetes management, and TIR data gives them the tools to have engaging and productive conversations with their providers.

Non-Pregnant Patients
Glucose RangeType 1 & Type 2 DiabetesOlder/High-Risk Diabetes
>250 mg/dL (13.9 mmol/L)<5%<10%
>180 mg/dL (10.0 mmol/L)*<25%<50%
70–180 mg/dL (3.9–10.0 mmol/L)>70%>50%
<70 mg/dL (3.9 mmol/L)**<4%<1%
<54 mg/dL (3.0 mmol/L)<1%
Pregnant Patients
Glucose RangeType 1 DiabetesGestational & Type 2 Diabetes#
>140 mg/dL (7.8 mmol/L)<25%
63–140 mg/dL (3.5–7.8 mmol/L)>70%
<65 mg/dL (3.5 mmol/L)<4%
<54 mg/dL (3.0 mmol/L)<1%

Hospital Use

Currently, continuous glucose monitoring (CGM) devices are not formally approved for in-hospital use. However, during the COVID-19 pandemic, U.S. regulators allowed their use under certain conditions to reduce the need for personal protective equipment and minimize exposure risks for healthcare personnel. As a result, interest in hospital-based CGM has grown, especially since more patients now arrive wearing the same devices they use at home. Recent clinical trials suggest CGM is safe to use on general wards and might help reduce low blood sugar events. In critical care units, concerns about factors like edema, poor blood flow, and acidosis affecting CGM accuracy remain, though preliminary research indicates that CGM—when combined with periodic conventional point-of-care (POC) glucose tests—can be safe and reduce the number of required fingerstick tests.

A panel of inpatient diabetes experts convened to discuss and outline the potential advantages of CGM in the hospital. They noted that CGM might be particularly helpful for patients who cannot communicate or recognize symptoms of low blood sugar. However, several issues limit routine inpatient use of CGM devices, including:

  • Concerns regarding accuracy in the low glucose range or in the presence of conditions such as diabetic ketoacidosis, impaired blood flow, or the use of certain medications.
  • Limited clinical support systems and workflows for integrating CGM data into standard care.
  • Unclear protocols for storing, displaying, and documenting CGM readings in electronic health records.

The group advised the following for patients who are admitted to the hospital while already using CGM devices:

  • Patients should be allowed to continue using their personal devices only if they can fully manage them without extra staff assistance and have appropriate supervision (e.g., by an endocrinologist or clinician trained in CGM).
  • Fingerstick or blood-based glucose checks must still be performed; hospitals should not rely exclusively on CGM for dosing insulin.
  • Hospitals are encouraged to develop written policies to address device management, safety concerns, liability waivers, and guidelines for calibrating or checking CGM readings.
  • CGM sensors must be removed before MRIs or CT scans.

Practical considerations for hospital use include:

  1. Implementing CGM to reduce staff exposure and personal protective equipment usage for highly contagious patients.
  2. Confirming CGM readings with POC testing before making treatment decisions, unless mitigating circumstances (e.g., severe infection risk) require alternative approaches.
  3. Creating workflows, educational materials, and hospital order sets to support CGM usage.
  4. Training nurses to check insertion sites each shift, recognize physical compression of sensors, and be alert to any interference from supplements or medications.
  5. Developing secure methods for managing and storing CGM data, distinguishing them from conventional glucose measurements, and noting the device identifier in patient records.

Limitations of Use

Clinical studies often recruit highly motivated participants, which may not reflect the broader population where people have varying levels of resources and commitment to technology use. In practice, potential barriers include cost, insurance coverage, difficulty learning to interpret extra data, and aversion to wearing a device. Although CGM use has increased substantially—particularly among people with type 1 diabetes—many cite expense and coverage issues as persistent obstacles. Disparities in prescribing also exist, with concerns about bias or unequal access.

Adherence to CGM can be hampered by practical issues. Some users discontinue because of skin irritation or sensor adhesion problems. Approaches such as barrier sprays or overlay patches may help, but better data and more research on these methods are needed. In addition, real-world studies show that long-term use rates can be modest; however, those who remain engaged often achieve better glucose control and experience fewer hospital admissions.

Another challenge is that certain substances—such as acetaminophen or vitamin C—may interfere with CGMs based on glucose-oxidase reactions. Devices also depend on sensor chemistry and can be susceptible to time delays in measuring glucose in the fluid between cells versus in the bloodstream. Although this delay is generally brief, it can matter for immediate treatment decisions.


Daily Use

Patients must recognize that CGM readings may differ temporarily from actual blood glucose, especially when glucose is changing rapidly after a meal or during exercise. For devices requiring calibration, it should not occur during fast-rising or rapidly falling glucose levels to avoid skewing results. Even when devices are approved for taking direct action on sensor readings, some users may opt for fingerstick confirmation (for instance, before correcting a high or low glucose) for extra security.

Alarm thresholds should be set thoughtfully so that patients respond effectively to potential problems without being overwhelmed by false alerts. False positives can erode trust in alarms, whereas thresholds set too high or too low may either over-warn or under-warn.

Several published algorithms address how best to respond to CGM alerts and trend arrows, though they can be complex and are often not integrated directly into insulin pump bolus calculators. These algorithms typically require patient familiarity with insulin action times, the possibility of stacked insulin doses, and the understanding that CGM trend predictions may be less reliable right after meals. Automated insulin-delivery systems aim to reduce this complexity by adjusting insulin based on CGM data in the background, with less user intervention.


Comparison of Personal CGM Systems

Many personal CGM systems—including real-time and intermittently scanned options—have gained regulatory clearance, with notable improvements in user experience over the years. The first device was approved in 2004, and since then, additional companies have introduced products. Sensor life has steadily increased, accuracy has improved, and calibration requirements have been reduced or removed in some newer designs.

Generally, each device differs in terms of:

  • Whether daily calibration is needed.
  • Whether confirmatory fingersticks are required before treatments.
  • Real-time alerts and the types of alarms available.
  • Sensor wear duration and warm-up times.
  • Compatibility with imaging equipment or susceptibility to interference from specific medications or supplements.

Regardless of model, all CGMs share basic limitations, including potential sensor lag times and the need for user troubleshooting if readings do not match expectations. However, with ongoing refinements and the development of robust training materials, CGM use continues to expand as more individuals see the benefits of detailed glucose trend insights.

Insurance coverage limitations

Diabetes prevalence: One might assume that states with the highest diabetes prevalence would invest more in diabetes tools, but this is not always the case. Out of the 14 states where at least 12% of adults have diabetes, only 6 of them (AR, NM, IN, OH, TX, and WV) provide Medicaid coverage for CGMs for individuals with both type 1 and type 2 diabetes.

Medicaid spending: Among the top 10 states with the highest Medicaid spending (exceeding $15 billion in total), five do not cover CGMs for people with both type 1 and type 2 diabetes. This approach is not cost-effective, as CGMs represent only 1.1% of the total cost of diabetes, while expenses related to treating complications and lost productivity—both of which would be reduced through widespread CGM use—account for 73.1% of total diabetes costs. Moreover, using a CGM is cost-effective for individuals with diabetes.

Future developments in CGM technology.

In this modern world, everything makes a progress fast, so what are the expectations of the new technology?

PK Vitality, the company responsible for creating the K’Watch Glucose blood sugar monitor, has shared the outcomes of a recent clinical trial. The continuous glucose monitor (CGM) smartwatch demonstrated a high accuracy level. The device employs a combination of micro-points and biosensors to measure blood glucose levels without causing pain. In its first trial, the K’Watch Glucose CGM smartwatch had a Mean Absolute Relative Difference (MARD) of 29% for accuracy, which the developers managed to reduce to 19% in the second trial. The third trial yielded a MARD level of 16%, with modifications to the measuring algorithm and refinements to the K’apsul patch contributing to this promising accuracy level. What millions of people with diabetes, who are weary of using lancets and test strips, want to know is when the device will be available, its cost, and whether it will be covered by insurance.

Conclusion

Technological progress in glucose monitoring is dynamic, ushering in a new era of data-driven diabetes management. Whether used in a professional context or as a personal tool, CGM delivers vast amounts of information about short-term and long-term glycemic patterns. Linking CGM data to smartphone apps and other software can significantly enhance patient engagement, communication, and therapy decisions. While alternative biomarkers and fully autonomous insulin-delivery systems continue to develop, CGM has already reshaped diabetes care by improving safety and control for a broad range of individuals managing this condition.

References

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About the Author MyEndoConsult

The MyEndoconsult Team. A group of physicians dedicated to endocrinology and internal medicine education.

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