Are Glucose Readings different between CGM and BGM?

Are Glucose Readings different between CGM and BGM?

Both Continuous Glucose Monitoring (CGM) and Blood Glucose Meters (BGM) are systems used by diabetics to measure and monitor the glucose levels in their body.

Even though both are sufficient and efficient when it comes to diabetes management and monitoring, there is a substantial difference between the two. We’ll get into the finer details of the matter in this article but to keep it simple: a Continuous Glucose Monitoring system measures the glucose levels in the interstitial fluid throughout the day and night while a Blood Glucose Meter measures the glucose levels in the blood at a single moment in time.

The difference between CGM and BGM

Another significant difference between the systems is that glucose readings and measurements are taken differently between the two systems.

Continuous Glucose Monitoring makes use of a sensor that is placed under the skin of the upper arm and connected to a transmitter—which then sends glucose readings at regular intervals to a handheld reader through Bluetooth technology.

On the other hand, Blood Glucose Meter needs a fingerstick that pricks the fingertip to measure glucose levels.

The frequency of reading also spreads the gap even larger between the two systems.

Continuous Glucose Monitoring systems provide readings by using the data that has been collected over an entire night and day while a Blood Glucose Meter is only capable of providing a single reading of glucose levels.

Since Continuous Glucose monitoring systems collect readings throughout the day and night, it’s safe to say that they can give dynamic information regarding the rate of change and direction of glucose levels. This sort of trajectory can help the person managing their diabetes make the necessary changes to keep their glucose in check.

Blood Glucose Meter systems don’t have this level of proactivity.

Continuous Glucose Monitoring systems are best used to manage outpatient glycemic to reduce AIC and also helps with reducing the guesswork that normally happens when making decisions for treatment based on a single reading from a blood glucose meter.

Blood Glucose Meter systems require deliberate action such as calibration to get glucose level readings while Continuous Glucose Monitoring system gives readings in real-time even when the patient is sleeping as it works throughout the night.

Continuous Glucose Monitoring System

CGMs have various benefits and shortcomings when measuring and monitoring glucose levels:


CGMs provide a trend of glucose level readings in real-time, which not only tells you where the glucose levels are headed but also where it is at the time.

This gives you the information to manage the glucose levels around physical activities and food.

Since CGMs measure glucose levels at all times, the system can detect the highs and lows that the patients may miss and notifies them through programmed alerts.

This is beneficial for any patient but especially for parents who have diabetic children that may not be able to communicate when their glucose levels are low or high.

CGMs also allow for viewing of the glucose levels from a distance as the transmitter can send the data to the receiver a few feet away. This makes it easier for parents and caregivers to check the glucose levels on their reader or smartphone without necessarily being with the patient in the same room.

The use of CGMs allows for pattern detection on the glucose levels as it measures the levels throughout the day and night. This helps assess the effectiveness of the patient’s insulin doses and the possible effect that physical exercise and food can play on the glucose levels.


However, a CGM can be a technological burden to some patients and caregivers as it is a new thing to learn and wear, which can make daily life seem more complicated.

CGMs may lead to data overload, since it provides a lot of information regarding glucose levels—more than the patient has ever had before.

Since CGMs involves placing a sensor under the skin, which may be uncomfortable to wear and can cause pain.

Who should use a CGM?

The American College of Endocrinology (ACE) and American Association of Clinical Endocrinologists (AACE) has published guidelines that recommend the following patients to use CGM:

  • Patients that are unaware of hypoglycemia or/and are at high risk of hypoglycemia.
  • Patients with type 2 diabetes on basal insulin, multiple insulin injections or sulfonylureas.
  • Patients with type 1 diabetes.

Blood Glucose Meter System

BGMs have various advantages and disadvantages when monitoring glucose levels of patients.


When used properly, BGMs give accurate readings of the blood glucose levels.

Most traditional Blood Glucose Meters are affordable and often covered by insurance companies.

After years of development, most Blood Glucose Meter manufacturers’ have been able to make them less complicated and easy to use.

Blood Glucose Meters are versatile as they provide a variety of extras. Most meters store results of past tests in the internal memory and the patient can download the data into a personal computer for recordkeeping.


BGMs are invasive as the patient needs to draw blood whenever they want to check their glucose levels by pricking their fingertips or other less sensitive areas.

BGMs only provide a snapshot of the glucose levels at that particular time. For the patient to know how the glucose levels fluctuate, they need to do many tests throughout the day.

The strips used by the BGMs are not interchangeable. This means that the patient must use strips that are designed for the specific meter, if not, the readings may not be reliable.

Who should use a BGM?

Patients with Type 1 diabetes can use BGM to measure their glucose levels 4 to 10 times a day.

Patients with Type 2 Diabetes need to use BGM 2 to 4 times per day to measure their glucose levels.


Before deciding on whether to use Continuous Glucose Monitoring system or Blood Glucose Meter to measure your glucose levels, consult your doctor to give you the best advice.

If the glucose alerts and readings from the Continuous Glucose Monitoring system do not match the symptoms that you are experiencing or expectations, use a Blood Glucose Monitor to make any decisions involving diabetes treatment.


If you are not insured, or have a high deductible health insurance plan, you can still purchase the Freestyle Libre Reader and Sensors at extremely competitive prices. Prices starting as low as $99 per month

*Fingersticks are required for treatment decisions when you see Check Blood Glucose symbol, when symptoms do not match system readings when you suspect readings may be in accurate, or when you experience symptoms that may be due to high or low blood glucose.

Reference 1: Data on file. Abbott Diabetes Care. 2, FreeStyle Libre 14 day User’s Manual

Indications and Important Safety Information

FreeStyle Libre and FreeStyle Libre 14 day Flash Glucose Monitoring systems are continuous glucose monitoring (CGM) devices indicated for replacing blood glucose testing and detecting trends and tracking patterns aiding in the detection of episodes of hyperglycemia and hypoglycemia, facilitating both acute and long-term therapy adjustments in persons (age 18 and older) with diabetes. The systems are intended for single patient use and require a prescription.

CONTRAINDICATIONS: Remove the sensor before MRI, CT scan, X-ray, or diathermy treatment.

WARNINGS/LIMITATIONS: Do not ignore symptoms that may be due to low or high blood glucose, hypoglycemic unawareness, or dehydration. Check sensor glucose readings with a blood glucose meter when Check Blood Glucose symbol appears, when symptoms do not match system readings, or when readings are suspected to be inaccurate. The system does not have alarms unless the sensor is scanned, and the system contains small parts that may be dangerous if swallowed. The system is not approved for pregnant women, persons on dialysis, or critically-ill population. Sensor placement is not approved for sites other than the back of the arm and standard precautions for transmission of blood borne pathogens should be taken. The built-in blood glucose meter is not for use on dehydrated, hypotensive, in shock, hyperglycemic-hyperosmolar state, with or without ketosis, neonates, critically-ill patients, or for diagnosis or screening of diabetes. When using FreeStyle LibreLink app, access to a blood glucose monitoring system is required as the app does not provide one. Review all product information before use or contact Abbott Toll Free (855-632-8658) or visit for detailed indications for use and safety information.html. . FreeStyle, Libre, and related brand marks are trademarks of Abbott Diabetes Care Inc. in various jurisdictions. Other trademarks are the property of their respective owners. ©2018 Abbott. ADC-09691 vLO 10/18

*The FreeStyle LibreLink app and the FreeStyle Libre 14 day reader have similar but not identical features. Fingersticks are required for treatment decisions when you see Check Blood Glucose symbol, when symptoms do not match system readings, when you suspect readings may be inaccurate, or when you experience symptoms that may be due to high or low blood glucose.

The FreeStyle Libre 2 app and the FreeStyle Libre 2 reader have similar but not identical features. Fingersticks are required for treatment decisions when you see Check Blood Glucose symbol and when your glucose alarms and readings from the system do not match symptoms or expectations

‡‡‡Based on the sensor being replaced once every 14 days, and scanned at least once every 8 hours.

§§§Glucose readings are not available during 1-hour warm-up, when sensor is too hot or too cold, when you see an error or "LO" or "HI" message, or no current glucose reading