Better Blood Sugar Management with CGM Alerts

People living with type 1 diabetes (T1D) need to inject insulin to control their blood sugar and are faced with the daily challenge of avoiding both hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar). 

Some continuous glucose monitoring (CGM) systems (Medtronic, Dexcom) will send a sound and/or vibration alert when blood sugar variations require attention.  

The Flash system (FreeStyle Libre) does not provide similar alerts because it does not receive information automatically. So, there is no way to be warned about hypoglycemia or hyperglycemia; the blood sugar value is displayed only when the sensor is scanned.

The University of Utah recently analyzed the impact of the programmed alert thresholds on diabetes control for people with type 1 diabetes.

A higher than 4 mmol/L alert threshold to prevent hypoglycemia

The study found that a 4.2 mmol/L alert threshold was the most effective for reducing the frequency of hypoglycemia episodes (when blood sugar is lower than 4.0 mmol/L).

What about hyperglycemia?

As for hyperglycemia, the study found that the most effective alert threshold to both reduce high blood sugar episodes and stay within general recommendations is 9.4 mmol/L.  

This threshold was also found to promote hemoglobin A1c (A1c) results of 7% or less and a percentage of time spent in hyperglycemia of less than 5%.

Alert fatigue

Participants who used a higher hypoglycemia threshold did not receive more alerts; however, those who set a lower hyperglycemia threshold did experience more alerts. 

If your alert thresholds are too tight, you’ll likely receive more alerts that will interrupt your daily life, which could cause alert fatigue. This might make you want to stop using your CGM despite the benefits it brings you.

This is why it’s important to set an appropriate threshold. For example, start with a higher hyperglycemia threshold and adjust it gradually until you find the right balance between reaching your target blood sugar levels and a reasonable number of alerts. 

The BETTER project aims to understand the major issues and maximize the benefits of new treatments and technology for people living with type 1 diabetes.  

Do you live with type 1 diabetes?

Help us advance research, technology and treatment; register at www.type1better.com.


  • Lin, Y. K. et al. (2019). Alarm Settings of Continuous Glucose Monitoring Systems and Associations to Glucose Outcomes in Type 1 Diabetes, Journal of the Endocrine Society, doi: 10.1210/jendso/bvz005. 
  • Shivers, Joseph P. et al. (2013). « Turn it Off! »: Diabetes Device Alarm Fatigue Considerations for the Present and the Future, Journal of Diabetes Science and Technology, vol. 7(3): 789–794. 

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