What is Continuous Glucose Monitoring?

Introducing CGM

A Continuous Glucose Monitoring system, also called CGM, is a way to measure blood sugar for people with diabetes. It is a device that is typically worn on the back of the upper arm or stomach, and depending on the specific type, can check blood sugar levels every one to five minutes. If you do the math, this is 288 to 1440 readings per day! For the person using their glucose meter as recommended by their healthcare professional, CGM can provide much more data than traditional blood glucose meters.

In addition to more data, there are other differences between CGM and blood glucose meters (BGM). A reading taken by a finger stick using a glucose meter shows your blood sugar level at that moment in time, while CGM shows you the number AND the direction that your blood sugar is going. Imagine having a blood sugar of 100 mg/dL and thinking everything is fine because you are in target range, but not realizing that your blood sugar is dropping. This could become a dangerous situation especially if you don’t feel the usual symptoms of low blood sugar. CGM will display arrows to indicate if blood sugar is dropping and can even show the rate at which it is decreasing. For example, some CGM devices will use one or two arrows pointing down to indicate that blood sugar could drop, typically by more than 60 to 90mg/dL in the next 30 minutes. This information can help a person with diabetes know when to eat to prevent low blood sugar before doing a critical activity, like driving.

There are both professional CGM devices, owned by the clinic and available on a short-term basis, and personal CGM devices, which are owned by the person with diabetes and worn on a long-term basis.

How Does CGM Work?

CGM contains 3 parts: a sensor, transmitter, and receiver, also called a reader. The sensor is worn on the upper arm or stomach at least two inches away from the belly button. Each system has their own technique on where to place the sensor and how to insert it. This usually involves a simple one or two button press. There is a tiny wire included with the sensor that stays under the skin in the area called interstitial fluid. This is where CGM measures the blood sugar level and is actually above the capillary space, so it goes less deep than a lancing device used with a glucose meter. The transmitter goes on top of the sensor and is what transmits the blood sugar readings to a receiver. Some of the devices have a combined transmitter and sensor, while others require an additional step of attaching the transmitter. Readings are viewed on the receiver. With every device, there is an option to download a mobile application (app) and have the mobile device serve as the receiver. The sensor is worn for 7-14 days depending on the device. After that, a new sensor is re-inserted by the person with diabetes or their caregiver.

There are also intermittently scanned devices that require a scan to view the blood sugar reading. Other devices are considered real time and the blood sugar reading is always available as long as it is within 20 feet of the receiver.

Data can also be downloaded by your doctor’s office. The data is downloaded by plugging in the receiver via a USB. If using a mobile app, the data can be connected to the clinic’s data management system via Bluetooth®. In addition to sharing data with the clinic, many devices have mobile apps that allow you to share data with family members, friends, and significant others.

Benefits and Limitations to CGM

CGM captures the direct effects of food, physical activity, stress, and medications on blood sugar levels, allowing people with diabetes and their care team to quickly identify if any management changes are needed. The alerts for high and low blood sugar can be lifesaving, and typically improve time spent in target range. This can reduce the risk of diabetes complications and improvements in diabetes-related quality of life. Some CGM devices are approved to make treatment decisions without finger sticks, which can be more convenient at times, such as when dining in a restaurant.

Some people may feel continuous alerts can be disruptive if the CGM is not adjusted to the right setting. For instance, if the CGM has a high alert setting at 150mg/dL it is likely to go off almost every time a person eats. Healthcare teams can help determine the best setting alerts so that they are helpful and not disruptive.

Why is CGM Important

Studies have shown that people are more likely to achieve their A1C targets with more frequent blood sugar monitoring, which can lead to improved clinical outcomes. Low blood sugar alerts can be lifesaving, and provide piece of mind for people living with diabetes and their loved ones.

Products and reference designs of Continuous glucose monitor aggregator

Battery management

The energy storage subsystem performs battery gauging and authentication functions while charging the battery. Battery management includes Battery charger ICs、Battery protectors、Battery fuel gauges, the Corresponding products are BQ25185、BQ24133、BQ294502、BQ27427

Low voltage power supply

The non-isolated power supply subsystem provides the point-of-load power for the other devices (processor, analog circuitry, etc.). Low voltage power supply includes Boost converters (integrated switch)、Linear & low-dropout (LDO) regulators、Buck-boost, inverting & split-rail converters (integrated switch)、Load switches、Buck converters (integrated switch), the Corresponding products are TPS61087、TPS7A25、TPS63036、TPS22915、TPS62843

Calibration & authentication

The calibration and authentication subsystem verifies the authenticity of the sensor strips and does calibration when required. Calibration & authentication includes Battery authentication ICs, the Corresponding product is BQ2028

Line protection

The signal input/output protection subsystem protects the sensor front-end circuitry and sensor strips from ESD damage. Line protection includes ESD protection diodes, the Corresponding products are TPD2E001、TPD4E05U06、TPD4S012

Sensor front end

The analog front-end subsystem contains DAC, ADC, TIA and other functions. The test strips have electrodes where a precise bias voltage is applied with a DAC, and a current proportional to the glucose in the blood is measured as a result of the electrochemical reaction on the test strip. The current is usually converted to a voltage by a transimpedance amplifier (TIA) for measurement with an (ADC). Sensor front end includes General-purpose op amps、Comparators、Precision op amps (Vos<1mV)、Analog switches & muxes、Precision ADCs、Digital temperature sensors、Analog temperature sensors, the Corresponding products are LMC6442、TLV3201、OPA320、TS3A5017、ADS1113、TMP103、LMT70

Wireless interface

The wireless interface subsystem connects the system to the sensor/patch as well as devices like mobile phone, computers, etc. The interface can be NFC, Bluetooth, BLE, WiFi. Wireless interface includes Wi-Fi products、Low-power 2.4-GHz products、Sub-1 GHz transceivers、Other wireless products、Sub-1 GHz wireless MCUs, the Corresponding products are CC3301、CC2651R3、CC110L、RF430CL330H、CC1312R

Clocking

The clocking subsystem consists of clock frequency generation as well as a real-time-clock for time-keeping. Clocking includes Real-time clocks (RTCs) & timers, the Corresponding products are TPL5100、TPL5111

Digital processing

The digital processing subsystem includes control of the system and processing of sensed signals. Digital processing includes Wi-Fi products、MSP430 microcontrollers, the Corresponding products are CC3301、MSP430G2452

Output user interface

The output user interface subsystem consists of display, speakers, interface to memory card for data storage, etc. Output user interface includes ESD protection diodes, the Corresponding products are TPD2E001、TPD4S012

Input user interface

The input user interface subsystem includes a keypad, touchscreen controller, capacitance-to-digital converters, inductance-to-digital converters, haptic drivers, and analog inputs like microphones. Input user interface includes Signal conditioners、Inductive sensor AFEs、MSP430 microcontrollers、Haptic motor drivers、Piezo drivers, the Corresponding products are LMP91000、LDC1314、MSP430F1612、DRV2605、DRV2667

Wired interface

The wired interface subsystem is used to connect the system to a computer for data transfer through various interfaces like USB, Ethernet, RS-232. This subsystem also provides analog outputs for field processing. Wired interface includes General-purpose op amps、ESD protection diodes、USB Type-C & USB Power Delivery ICs, the Corresponding products are LMC6442、TPD4E05U06、TPS25730