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CGM vs. BGM: A Comprehensive Comparison for Choosing the Best Monitor

Madison Holt, MS, RDN, LD

Published in CGMs and Sensors

6 min read

December 3, 2020
May 23, 2023
someone using a cgm app and a bgm
someone using a cgm app and a bgm

Maintaining optimum blood glucose levels is key to keeping your body healthy. Glucose levels fluctuate throughout the day for everyone, but it's not just your diet that affects your glucose level.

Exercise, hormones, sleep patterns, meal timings, medication, and stress all have an impact as well. However, keeping blood glucose levels within the optimum range is not always that simple and it can be challenging for many people.

In Western lifestyle, glucose intolerance is becoming more prevalent every year. If your blood glucose levels are higher than average, but not high enough to be classified as diabetic, this may be diagnosed as glucose intolerance (also known as prediabetes).

In fact, 88 million American adults have prediabetes, but 84 percent of them do not know they have it. A simple solution to help you better understand your blood glucose levels is to wear a continuous glucose monitor (CGM).

A CGM can help you identify sudden drops or increases in glucose levels, and understand causes of the fluctuations. This article will discuss what a is a CGM device, how it differs from other blood glucose monitors, the practicalities of wearing a CGM sensor and why a CGM is beneficial to your overall metabolic health.


What is the Difference Between Blood Sugar Levels and Glucose Levels?

Firstly, it's important to clear up that blood sugar levels and blood glucose levels are the same. Blood sugar (also known as blood glucose) is a type of sugar found in your blood. The two terms are often used interchangeably, so you may see information referring to either blood sugar levels or blood glucose levels.

If you don't have any symptoms or have never used a glucose monitoring device before, it's likely that you may not even know if your glucose levels are consistently high. There's a chance that you may have unawareness of your glucose intolerance, which can lead to serious health issues if left unchecked.

What is a Continuous Glucose Monitoring System?

a woman scanning her continuous glucose monitor

A continuous glucose monitoring system measures and continuously stores glucose data. The CGM itself is a small device that you wear on the back of your arm for seven to 14 days. It tracks your glucose levels in real-time. You're able to actively see what is causing your glucose levels to dip and spike, helping to prevent severe hypoglycemia or hyperglycemia.

What is the Difference Between a CGM vs BGM?

A CGM measures the glucose level in your interstitial fluid, or glucose level in the fluid between the cells. A BGM, or blood glucose meter, works differently, as it involves collecting a blood sample to measure the glucose level in your blood.

A CGM records continuous measurements, since it is inserted directly into your arm and worn for up to two weeks at a time. In comparison, blood glucose monitoring is only capable of recording a snapshot in time, so ongoing trends in glucose fluctuations throughout the day are not able to be seen.

Since these two devices measure glucose levels in two different areas of your body, the results will not match up precisely if taken simultaneously.

a CGM and a BGM

CGM glucose monitoring systems work through a tiny sensor inserted under your skin. The device comes with a spring-loaded applicator that applies the sensor quickly to the back of your arm. The CGM reads your glucose measurements and automatically sends the data to your phone or tracking app.

A BGM monitor, on the other hand, requires you prick your finger using a fingerstick and apply a drop of blood to a test strip in the BGM. The BGM then measures your blood glucose level showing a reading on the screen of a measuring device.

Benefits of a CGM vs BGM

There are many benefits to using a CGM, including:

  • Being able to make informed decisions about how to balance your food, physical activity, and stress levels based on real-time glucose level responses.
  • Experiencing fewer emergencies related to low glucose, since a CGM can predict low blood glucose approximately 20-30 minutes before it happens.
  • Less invasive as there is no need for constant finger pricking, which is required when using a BGM.
  • You can download real-time data onto your phone to actively track your glucose trends.

What is the Difference Between a CGM and FGM?

A flash glucose monitor (FGM) is a technologically advanced version of a CGM system that does not require calibration. Scientists state that factory calibration is possible due to the highly developed technology. CGMs usually require calibrating, sometimes twice a day.

Calibration requires the use of a BGM, so you need to have both devices. However, this is not necessary with a FGM. An example of a FGM is the Freestyle Libre system. Rather than continuously sending data automatically, it provides a reading when the user scans the sensor with their enabled smartphone.

Although referred to as a CGM, the cutting edge technology of the Freestyle Libre FGM avoids the need for a BGM and continual calibration of glucose levels.

How Long Can You Wear a CGM?

a man wearing a cgm with a NS patch

The CGM sensor captures glucose levels continuously for 14 days. It is for one-time use only. Discard the sensor at the end of the 14 day period.

Is the CGM Waterproof?

The CGM is not entirely waterproof, but it is water-resistant. This means that the sensor will remain on your body and not be affected in the shower or during a gym workout. You can even wear it in a sauna.

However, swimming and keeping the sensor underwater for more than 30 minutes is not recommended and may cause it to malfunction. It is advised that the sensor does not go below three feet of water, and it has not been tested in seawater. To ensure the sensor stays in place, it is advisable to wear a bandage over the top.

Who Needs Continuous Glucose Monitoring?

Mistakenly, many people think that continuous glucose monitoring is just for people with diabetes. This is far from the truth. Going beyond diabetes treatment, continuous glucose monitoring is beneficial for anyone wanting to:

  • Optimize their health
  • Develop a personalized nutrition plan
  • Understand the effect of lifestyle factors on blood glucose
  • Take control of their blood glucose levels
  • Focus on preventative health
  • Improve glycemic control and reduce their risk due to prediabetes or type 2 diabetes
  • Take control of their diabetes management
  • Have a discreet diabetes care system
  • Optimize performance and see the results of specific diets (e.g., athletes, ketogenic)

Why Choose a CGM system?

a man logging his meal in the Nutrisense app, wearing a CGM

When looking at the differences between a BGM vs. CGM, the CGM system is an efficient and effective form of blood glucose monitoring in the home environment. It puts you in control of your own body. It has shown to reduce the risks of severe hypoglycemia, hyperglycemia, and glycemic variability.

Whereas traditional BGMs require a finger prick, this is not necessary with the Freestyle Libre CGM system, making measuring blood glucose values discreet and comfortable, and reducing the risk of infection.

By having access to real-time glucose level readings, you can discover how your body responds to diet, exercise, sleep, stress, and medication. This allows you to build a personalized nutrition plan and lifestyle routine to optimize your health.
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Engage with Your Blood Glucose Levels with Nutrisense

Your blood sugar levels can significantly impact how your body feels and functions. That’s why stable blood glucose levels can be an important factor in supporting overall wellbeing.

With Nutrisense, you’ll be able to track your blood glucose levels over time using a CGM, so you can make lifestyle choices that support healthy living.

When you join the Nutrisense CGM program, our team of credentialed dietitians and nutritionists are available for additional support and guidance to help you reach your goals.

Ready to take the first step? Start with our quiz to see how Nutrisense can support your health.

Find the right Nutrisense program    to help you discover and reach your health potential.
Kara Collier, RDN, LDN, CNSC

Reviewed by: Kara Collier, RDN, LDN, CNSC

Kara Collier is the co-founder and VP of Health at Nutrisense, one of America’s fastest-growing wellness-tech startups, where she leads the health team. She is a Forbes 30 under 30 recipient, frequent podcast guest & conference speaker.

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