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

These devices can be a useful and convenient way to help manage blood sugar levels in diabetes.

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 they can place on their bodies 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 effect 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. Additionally, 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 10–14 days.


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

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

Most systems can display readings that are close to real-time, although many systems have a 10–12-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.

A monitor shows the user’s 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:

  • individuals on intensive insulin therapy, which is also known as tight blood sugar control
  • those who may experience hypoglycemia unawareness, which refers to not experiencing the typical warning signs of low blood sugar
  • people who often have high or low blood glucose

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 the time in optimal blood sugar range
  • reduce the number of hypoglycemic events — when a person’s blood sugar level drops too low
  • decrease time spent with low blood sugar

A CGM may offer many benefits over other devices. It can help people better manage diabetes and improve health outcomes.

Elsewhere, a 2021 extension study investigated the potential long-term effects of using a CGM. The results suggest CGMs have a beneficial effect on HbA1C, hypoglycemia prevention, treatment satisfaction, well-being, and the person’s confidence in their ability to avoid hypoglycemia problems.

A 2021 study notes that a CGM device can improve health outcomes for both the pregnant individual and the fetus 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 someone with a recent diagnosis of diabetes. This is because 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 throughout the day and night
  • seeing levels at times that may be difficult to check, such as during the night
  • helping identify trends
  • less reliance on finger-prick checks
  • alarms notifying users of high and low levels

Considerations for continuous glucose monitors

Although a CGM can offer many benefits for people with diabetes, it may come with certain limitations, such as:

  • Price: CGM devices can also be costly, and some insurance plans may not cover them.
  • Finger-pricking: While it does reduce the number of finger-prick tests necessary, it does not eliminate them entirely. People may still require finger pricks to calibrate a CGM and confirm readings.
  • Risk of breakage: While the sensors are generally robust, people may also need 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.

This section answers some frequently asked questions about continuous glucose monitors.

How much does a CGM cost?

The cost of a CGM can vary depending on the manufacturer. One device currently on the market in the United States is a Dexcom G6.

The cost of a transmitter for a Dexcom G6 was around $422 in 2022, but sensors may incur additional costs as they need replacing every 10 days.

Other CGMs on the market include Medtronic Minimed Guardian Connect and the Abbott FreeStyle Libre 2. The prices of these devices and relevant equipment may vary, ranging from approximately $50 to $200.

Insurance may also help with the costs of a CGM device and equipment if a person has the appropriate cover.

A person can set up a monthly subscription for sensors and equipment for a CGM, which may reduce costs in the long run.

Can I get a continuous glucose monitor without a doctor?

Usually, a CGM requires a prescription, so a person will have to work with a healthcare professional to apply for one.

Management of diabetes involves strict control of blood sugar levels. A continuous glucose monitor (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.