Continuous Glucose Monitoring: Weighing the Pros and Cons

Woman wearing a CGM and putting her hair up

AzmanJaka / Getty Images

In This Article

Continuous glucose monitoring (CGM) devices provide real-time glucose readings 24 hours a day, thereby allowing patients with type 1 or type 2 diabetes to closely track blood sugar levels and trends. Typically, CGMs report blood sugar levels every five minutes, thereby providing 288 glucose readings per day. CGMs can help patients make better-informed blood sugar decisions by alleviating much of the guesswork about daily patterns and fluctuations.

How It Works

Most CGM devices consist of three parts:

  • A tiny sensor wire that is inserted under the skin using an automatic applicator to measure glucose levels. The sensor wire is held in place by an adhesive patch.
  • A transmitter attached to the sensor, which sends glucose level data wirelessly to a receiver.
  • A receiver attached to a monitor that displays glucose levels and trends.

Some devices use Bluetooth technology to submit blood glucose information directly to compatible smartphones, bypassing the need for a separate receiver.

Additionally, other CGM devices include user-friendly cloud-based reporting software. When blood glucose information is received by a smart device, it is then transmitted via the cloud to up to five selected followers. This information can then be easily accessed at the doctor’s office, facilitating the tracking and analysis of patterns and displaying trends in graphical form.

Some CGM devices allow you to input information about meals, snacks, medication, and physical activity to further help with tracking glucose trends.


Continuous glucose monitoring can make diabetes care easier by:

  • Helping detect trends in blood glucose levels, even if the measurements are not entirely precise. For example, CGMs can show early morning spikes or dips in blood glucose at times when most people aren’t checking sugars frequently.
  • Eliminating the need for numerous fingerpricks, which may be painful and difficult to manage frequently.
  • Helping to clarify the effect of diet and exercise on blood sugar levels.
  • Alerting users with an alarm when glucose levels are too low or too high.

What Research Says

In some large trials, CGMs lowered hemoglobin A1c anywhere from 0.3% to 1% when compared to traditional fingerstick glucose checks. Studies have also shown that CGMs may reduce the risks of hypoglycemia.

CGMs can also be used with insulin pump therapy. A sensor-augmented pump (SAP) combines the technology of an insulin pump with a continuous glucose sensor, allowing users to monitor both glucose and insulin levels simultaneously.

In a new development, researchers have successfully created the first closed-loop insulin delivery system, which combines CGM technology with an insulin pump and a special algorithm that allows the insulin pump and CGM to use glucose readings to calibrate insulin levels accordingly and then immediately deliver a specified amount automatically.


Despite the positives, continuous glucose monitoring has drawbacks that should be considered:

  • Although CGM delivers blood glucose readings automatically at short intervals, twice-daily fingersticks usually are necessary in order to calibrate the CGM for accurate readings.
  • CGM devices often yield lower glucose readings when compared to venous blood glucose.
  • There is data to suggest CGM may become increasingly inaccurate at low glucose ranges—even though the technology has been touted as being especially beneficial for detecting hypoglycemic episodes.
  • CGM machines are expensive, with initial costs ranging between $1,000 and $2,000, and are available by prescription only. In addition, supplies cost between $300 and $450 per month, including sensors that should be replaced every 3 to 7 days.

Specific Devices

Dexcom G5: The first FDA-approved CGM device for patients 2 and older, the Dexcom G5 works with an easy-to-use app, offers cloud storage, and syncs with both Android and iPhone operating systems. Requires twice-daily fingersticks for accurate calibration.

Dexcom G6: The Dexcom G6 is the first model approved for medical treatment decisions, meaning that your care provider can make changes to your diabetes treatment plan based on your CGM results alone—no fingersticks necessary. Other models required users to confirm CGM results with a fingerstick blood glucose test before making treatment changes. The G6 can predict both hypoglycemic and hyperglycemic trends. Sensors last 10 days before they must be changed.

Freestyle Libre: The first FDA-approved CGM device for people over 18, the Freestyle Libre eliminates the need for daily fingersticks except for the occasional device calibration. Users must scan the sensor at least once every eight hours—the device will not automatically alert you if your levels are too low or too high—it must be scanned in order to do so. Sensors last 14 days before they must be changed.

Medtronic Guardian Connect: The Medtronic Guardian Connect sensor may be worn up to seven days, though the transmitter lasts up to one year—which differs from other models that may need transmitters replaced as many as four times per year. The Guardian Connect CGM works closely with the Sugar.IQ diabetes assistant app, helping you monitor and keep track of your levels from a simple-to-use interface.

Who Should Use CGM

Patient selection is a key component to successful CGM use. The Endocrine Society Guidelines recommend CGM for adult patients with type 1 diabetes who have A1c levels above 7% and who have shown that they can use these devices nearly every day.

In addition, it is crucial to understand CGM technology in order to reap the maximum benefit. The intermittent use of CGM may be appropriate for patients with overnight hypoglycemic or hypoglycemic unawareness (inability to self-detect hypoglycemia). It may also be beneficial for patients with type 2 diabetes who have overnight hypoglycemia or frequent episodes or hypoglycemic unawareness.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lawton J, Blackburn M, Allen J, et al. Patients' and caregivers' experiences of using continuous glucose monitoring to support diabetes self-management: qualitative studyBMC Endocr Disord. 2018;18(1):12. Published 2018 Feb 20. doi:10.1186/s12902-018-0239-1

  2. National Institute of Diabetes and Digestive and Kidney Diseases. Managing Diabetes: Continuous Glucose Monitoring. Updated June 2017.

  3. Polonsky WH, Fisher L, Schikman CH, et al. Structured self-monitoring of blood glucose significantly reduces A1C levels in poorly controlled, noninsulin-treated type 2 diabetes: results from the Structured Testing Program studyDiabetes Care. 2011;34(2):262-267. doi:10.2337/dc10-1732

  4. Lucidi P, Porcellati F, Bolli GB, Fanelli CG. Real-time continuous glucose monitoring decreases the risk of severe hypoglycemia in people with type 1 diabetes and impaired awareness of hypoglycemiaAnn Transl Med. 2018;6(Suppl 2):S97. doi:10.21037/atm.2018.11.23

  5. Cengiz E, Tamborlane WV. A tale of two compartments: interstitial versus blood glucose monitoringDiabetes Technol Ther. 2009;11 Suppl 1(Suppl 1):S11-S16. doi:10.1089/dia.2009.0002

  6. Dungan K, Verma N. Monitoring Technologies – Continuous Glucose Monitoring, Mobile Technology, Biomarkers of Glycemic Control. [Updated 2018 Jan 10]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext. South Dartmouth (MA):, Inc.; 2000-. 

  7. Klonoff DC, Buckingham B, Christiansen JS, Montori VM, Tamborlane WV, Vigersky RA, Wolpert H. Continuous glucose monitoring: an endocrine society clinical practice guideline. The Journal of Clinical Endocrinology & Metabolism. 2011 Oct 1;96(10):2968-79.

Additional Reading