A continuous glucose monitor (CGM) is a medical device that monitors blood glucose throughout the day. It works by measuring fluid glucose levels via a small implant.

Diabetes is a condition that hinders the body’s ability to produce or use insulin. This hormone is responsible for enabling cells to use glucose in the blood as an energy source. To help manage this condition, people must control their blood glucose and aim to keep sugar levels within a healthy range.

Managing diabetes can be overwhelming. While necessary, regularly checking blood sugar can be inconvenient and tiring. However, technology such as continuous glucose monitors (CGMs) offer a practical option that may make it easier to monitor and control blood sugar.

In this article, we will explore how CGMs work and how they can help people manage diabetes.

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Continuous glucose monitoring refers to the ability to constantly measure a person’s blood glucose levels throughout the day and night. To achieve this, people can use a CGM, which is a wearable device that a person places on their body to quickly and easily check their blood sugar.

It can provide users with dynamic information about their blood sugar and can use alerts to warn the wearer of dangerous glucose levels. Using these devices can be a useful and convenient way to help people better manage diabetes. Evidence notes that these devices can have a positive impact on glycemic control and improve HbA1C levels.

Previously, one of the main options to test blood sugar was a blood sugar meter. However, this option was not practical for many people as it involved many components, and a person had to prick their finger to draw blood. Also, it would only provide a single reading at the time of taking the sample.

As such, CGMs can provide a more convenient and accessible way to monitor blood glucose.

Each CGM has three main parts: a sensor, a transmitter, and a monitor.


A CGM user inserts a small sensor directly under the skin, usually on the belly or arm. A thin tube, or cannula, pierces the top layer of skin and measures glucose in the interstitial fluid. This is the fluid that surrounds cells in the body and provides a similar reading to blood glucose.

Most sensors are waterproof and an adhesive patch keeps them firmly in place. Users will need to regularly replace the sensor, with most working for roughly 7–14 days.


The sensor connects to a transmitter that allows the system to wirelessly send blood glucose readings. The transmitter communicates with the sensor and monitor and passes on the information displayed on the monitor.

Many systems combine the sensor and transmitter, so a person may need to sync this part with their monitor to receive readings.

Most systems are able to display readings that are close to real time, although many systems have a 5-minute delay.


The monitor is responsible for displaying information to the user. Some CGMs have a dedicated monitor, which may be a separate device or part of an insulin pump. Other devices are smartphone-compatible and work via a smartphone app.

With a monitor, the user can see their blood sugar levels every few minutes. The CGM system can also store this information and send it to a doctor. The ease of collecting and sharing blood sugar levels can help doctors and CGM users work together on improving a diabetes treatment plan.

Typically, most people who use a CGM will have type 1 diabetes. Some individuals with type 2 diabetes may also benefit from CGMs.

A doctor may prescribe a CGM if people meet certain criteria and requirements. Usually, this may include:

For these individuals, a CGM can help them closely monitor blood sugar levels and may prevent them from experiencing a serious hypoglycemic event.

A 2020 commentary notes that a CGM can help:

  • increase time in optimal blood sugar range
  • reduce the number of hypoglycemic events
  • decrease time spent with low blood sugar

There are many benefits a CGM may offer over other devices. Namely, it can help people better manage diabetes and improve health outcomes.

A 2017 study highlights that CGMs can improve glycemic control in individuals with inadequately controlled type 1 diabetes. Compared with conventional treatment options, people using CGMs had lower HbA1C levels.

Elsewhere, a 2021 extension study investigated the potential long-term effects of using a CGM. The results suggest that CGMs have a beneficial effect on HbA1C, hypoglycemia prevention, hypoglycemic confidence, treatment satisfaction, and well-being.

A 2021 study notes that a CGM device can improve health outcomes for both parent and baby during pregnancy. A 2020 commentary also highlights CGMs as a reliable, safe, and effective tool, particularly during the COVID-19 pandemic.

Having a CGM may be particularly useful for a person with a recent diagnosis of diabetes as it can help them identify what triggers blood sugar changes and how to minimize these fluctuations.

Other advantages of a CGM may include:

  • continual tracking of sugar levels through the day and night
  • seeing levels at times that may be difficult to check, such as during the night
  • helping to identify trends
  • less reliance on finger-prick checks
  • alarms notifying users of high and low levels

This indicates that CGMs may show promise for individuals with diabetes across different ages and health considerations. As such, people with diabetes and their doctors can use a CGM to improve diabetes management strategies.

Although a CGM can offer many benefits for people with diabetes, it may come with certain limitations. While it does reduce the number of finger-prick tests needed, it does not eliminate them entirely. People may still require finger pricks to calibrate a CGM and confirm readings.

The cost of CGM devices can also be prohibitive for many users and some insurance plans may not cover them. This could result in the price of a CGM running higher than other testing devices.

While the sensors are generally robust, people may also want to avoid certain activities to prevent the risk of knocking or damaging the device, as they will need to replace it if it stops functioning.

Some people may also find the amount of data a CGM provides overwhelming. Understanding the information and making decisions from it may cause anxiety in some individuals.

Also known as an automated insulin delivery system or artificial pancreas, these systems can help mimic the function of a healthy pancreas. A CGM device is an important piece of a hybrid closed-loop system. These systems typically consist of three different components:

  • a continuous insulin pump below the skin
  • a CGM
  • a control algorithm

In this system, the CGM keeps track of the blood sugar at regular intervals. It sends information about blood sugar levels to the control algorithm. The control algorithm analyzes this information and then sends instructions to the insulin pump. This way, the pump can deliver an appropriate dose of insulin when necessary.

Many systems may only be compatible with basal, or slow-acting, insulin. In these cases, people will still need to calculate and manually administer bolus, or rapid-acting, insulin at certain times, such as with meals.

However, other systems, such as the Omnipod, can calculate and suggest a bolus dose using an algorithm and the CGM reading.

These systems can take the guesswork out of insulin injections during the day. Many users find them helpful for simplifying the process of blood sugar regulation.

Management of diabetes involves strict control of blood sugar levels. A CGM can help facilitate this by providing users with a quick and convenient way to monitor blood glucose. Evidence notes that these devices can aid glycemic control, prevent hypos, and improve overall health and well-being.

Individuals interested in using a CGM can consult with a medical professional about their suitability and how it may help with their health.