Pharmacy U

The case for Continuous Glucose Monitoring (CGM)


Many patients do not achieve their blood glucose targets using traditional self-monitoring of blood glucose (SMBG).


By Shelley Diamond, BScPhm


Continuous glucose monitoring (CGM) is a significant advance in that it provides real-time information about current glucose levels, trends and rates of change, allowing for proactive versus reactive interventions.

CGM repeatedly measures glucose in the interstitial fluid (every five minutes) to give ‘real-time’ glucose values throughout the day, and can provide trends of the direction of glucose levels over time. This allows for identification of fluctuations as a result of the glycemic effect of food, physical activity, insulin and medications that may not have been detected with SMBG.

A tiny glucose-sensing device, the ‘sensor,’ is inserted just under the skin on the abdomen, and is very similar to the insertion of an insulin pump catheter. The sensor is worn for six to seven days depending on the specific device. Glucose level readings are sent via radio waves to a pager-like wireless monitor that can be attached to a belt, carried in a pocket or hidden under clothing. For children, the monitor would be kept by the parent.

Blood glucose levels using a fingerstick still need to be done in order to calibrate the continuous glucose monitor two to four times per day.

Insulin, physical activity, and food eaten are recorded into the monitor by pushing a specific button. CGMs utilize real-time alarms for thresholds and predictions of hypo- and hyperglycemia, as well as rate of change alarms for rapid glycemic excursions.

Two devices available on the Canadian market are Enlite™ Glucose Sensor and Dexcom G4®. The Enlite system also includes a ‘low glucose suspend,’ system which provides feedback to the insulin pump and shuts off delivery at specific thresholds. For patients using the Dexcom G4, it is important to let them know that acetaminophen use may falsely raise sensor glucose readings.

Software is available to download data from the devices to a computer for tracking and analysis of patterns and trends. Learn more about these specific devices at or

Who can benefit from using CGM?

A recent systematic review and meta-analysis (*Poolsup et al. Diabetology & Metabolic Syndrome 2013, 5:39) concluded that ‘real-time’ CGM can be more effective than SMBG in reducing HbA1C for type 1 diabetes pediatric populations. CGM was also found to be superior to SMBG for adults with type 2 diabetes.

Situations where CGM might be considered include:

  • Patients who have the potential to have a dangerously low overnight blood glucose which might otherwise go undetected or general hypoglycemia unawareness
  • To reduce A1C targets without increasing hypoglycemic events
  • To detect early morning high blood glucose levels or those that occur between meals.
  • Pregnant women or women planning pregnancy
  • Children and adolescents with type 1 diabetes who are at or above their A1C targets

Continuous glucose monitoring is not for every patient with diabetes because of the training time and cost; however, many insurance plans are now covering this expense. CGM is not a replacement, rather it’s an adjunct for the blood glucose meter. It is also not a device to put on and ‘forget about’.

The future of CGM

We can look forward to the ‘closed-loop artificial pancreas system’ where insulin delivery will be fully automated. In the meantime, consider the current technology for your patients who would like to tighten glycemic control safely and ease the burden of diabetes self-management.


Shelley Diamond BScPhm is a pharmacist and President, Pedipharm Consultants and Co-founder/President, Diabetes Care Community Inc.