Continuous Glucose Monitoring (CGM) systems are medical devices that provide a comprehensive view of glucose levels throughout the day and night. These systems measure glucose in the interstitial fluid, the liquid found between cells, rather than directly in the blood. This continuous stream of data is a significant advancement over traditional fingerstick testing, which only provides a single point-in-time reading. For individuals managing conditions like diabetes, CGM devices are instrumental in identifying trends and making informed decisions about medication and lifestyle adjustments.
Comparing Sensor Technology and Lifespan
The CGM market features several leading systems, distinguished primarily by their wear durations. Two major self-applied, disposable sensors offer relatively short wear times for convenience, lasting either up to 10 days or up to 14 or 15 days. Both are applied using a simple, self-contained applicator that inserts a tiny filament beneath the skin, typically on the upper arm.
A third option is a long-term implantable sensor that can function for up to six months. This device requires a minor, in-office procedure for both insertion and removal by a trained healthcare provider. The extended lifespan of this model significantly reduces the frequency of sensor changes compared to the shorter-term patches.
Systems also differ based on the need for calibration using a traditional fingerstick blood glucose meter. One short-term sensor and the long-term implantable sensor require daily fingerstick checks for calibration and accuracy. The other self-applied sensor is factory-calibrated, eliminating the need for routine manual adjustments. All systems may still require a confirmatory fingerstick test if the sensor reading does not align with a user’s symptoms or expectations.
Data Access and Connectivity Features
The utility of CGM technology depends on how glucose data is accessed and shared. All modern personal CGM systems transmit data wirelessly to a compatible smartphone or a dedicated receiver unit. The two primary self-applied systems differ in transmission frequency: one streams a reading every five minutes, while the other provides a reading every minute, offering near-instantaneous updates.
The long-term implantable system also provides a real-time glucose value every five minutes, but requires a separate, rechargeable transmitter worn externally over the sensor site. This external transmitter communicates with the mobile app and provides discreet on-body vibration alerts for high or low glucose levels, even when the smartphone is not nearby.
All three systems include customizable alerts and alarms to warn of high or low glucose levels. These alerts can be predictive, notifying the user before a glucose value is projected to cross a critical threshold, allowing for proactive intervention. The systems also offer remote monitoring capabilities through companion applications, allowing users to securely share data with caregivers or healthcare providers.
Acquisition and Accessibility
Obtaining a personal CGM system requires a prescription from a licensed healthcare provider. The devices and their ongoing supplies, such as sensors and transmitters, are typically classified as Durable Medical Equipment (DME) by insurance providers. Insurance coverage is a key factor in accessibility, with policies varying widely between private carriers and government programs.
Medicare, for example, covers CGM systems for patients with diabetes who are treated with insulin or have a documented history of problematic hypoglycemia. To meet Medicare’s criteria, the system must be used with a dedicated receiver or a compatible insulin pump, as using a smartphone app alone is not sufficient. Patients are usually responsible for a portion of the cost, typically 20% of the approved amount, after the Part B deductible is met.
Beyond personal-use devices, “professional CGM” systems are distinct in purpose and acquisition. These systems are owned by a healthcare clinic and are prescribed for temporary, diagnostic use, often for seven to fourteen days. The data from these sensors is reviewed by the medical team to identify glucose patterns and inform treatment decisions, rather than for the patient’s day-to-day management.