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The Role of Continuous Glucose Monitoring in Glycemic Control

Jul 23, 2019
Editor: David L. Joffe, BSPharm, CDE, FACA

Author: Onyi Ibeji, PharmD. Candidate, LECOM School of Pharmacy

Continuous Glucose Monitoring (CGM) tracks glucose levels 24 hours a day, which can enable better glycemic control for patients.

While the search continues for better diabetes management, the emergence of continuous glucose monitoring (CGM) devices has become one of the important current advances in technology for diabetes care. Unlike blood and urine glucose measurement methods, with their potential to become a bothersome chore, CGM is designed to measure the amount of glucose in the interstitial fluid continuously around the clock, displaying the results with immediate information about glucose levels and its trends, which ultimately, leads to better long-term health outcomes.

A detailed review of selected research articles is being done with the aim to demonstrate a good understanding of how continuous glucose monitoring effectively helps in glycemic control.

In the study and management of diabetes, blood and urine glucose measurements have been critical for effective strategies on diabetes management, with measurement of glycated hemoglobin (HbA1c) as the traditional method for assessing glycemic control, though it has limitations.  HbA1c provides only an average of glucose levels over the past few months and does not reflect intra- and inter-day glycemic excursions that may lead to hypoglycemia or postprandial hyperglycemia episodes. It is unreliable in measurements of patients with anemia and hemoglobinopathies. Also, self-monitoring of blood glucose (SMBG) with a structured testing regimen improves glycemic control and quality of life but again, with limitations. It provides only a single point-in-time measurement, without any indication of the direction or rate of change of glucose levels, and oftentimes, it fails to detect nighttime and asymptomatic hypoglycemia.

The proper use of CGM offers real-time measurement of glucose levels, with results that might require immediate attention or provide information that can be used over a short or long period of time. According to Oliver Schnell, et al, real-time continuous glucose monitoring (rtCGM) and intermittent CGM (iCGM) have the ability to address many of the limitations seen in HbA1c testing and SMBG. Both rtCGM and iCGM facilitate monitoring the percentage of time spent within the glucose range of 3.9–10.0 mmol/L during a 24-h period (time in range).

CGM provides real-time measurement of glucose levels in interstitial fluids that notifies for hypoglycemia and hyperglycemia, at which point immediate restorative and further preventive actions can be taken for good glucose levels control. Again, the trends noted while using CGM offer the possibility to evaluate lifestyle, education, pharmacotherapy, nutritional therapy, physical activity, and adhesion to therapy, thereby providing major contributions at improving glycemic control.

In a study by Klemen Dovc, et al, with the objective to evaluate the correlation between CGM use and glucose variability in preschoolers with type 1 diabetes, 40 preschoolers <8 years old were followed for the observational period of 116 patient/years. The table below is the summary of the findings.





SD (mmol/L)

3.6 (3.2–3.9)

4.3 (3.8–4.7)

SD (mg/dL)

64.8 (57.6–70.2)

77.4 (68.4–84.6)

Mean glucose (mmol/L)

9.4 (8.7–10.2)

9.3 (7.9–10.1)

Mean glucose (mg/dl)

169.2 (156.6–183.6)

167.3 (142.2–181.8)

HbA1c (%)

7.6 (7.2–8.0)

7.7 (7.2–8.0)

HbA1c (mmol/mol)

59.6 (55.2–63.9)

60.7 (55.2–63.9)


This result demonstrates that the use of CGM can improve glycemic control, reducing the glucose fluctuations due to frequent real-time insulin adjustments based on CGM device recorded sensor glucose trends. Secondly, this demonstrated CGM efficacy is also correlated with its frequency of use. The near-daily CGM users were seen to have a greater reduction in HbA1c when compared with the less frequent CGM users. Up to five days per week CGM usage was associated with a significant decrease in HbA1c by 0.4% [4.4 mmol/mol].

These two (HbA1c and SMBG) methods of assessing glycemic control have remained useful in diabetic care, but introduction of CGM in the assessment of glycemic status represents a huge technological advance for optimal glycemic control.

Practice Pearls:

  • Studies have shown that use of CGM improves glycemic control, reduces episodes of hypoglycemia and hyperglycemia, improves HbA1c and quality of life.
  • Continuous glucose monitoring provides valuable information on glycemic variability, patterns of glycemic excursions, and high or low glucose concentration tendencies that are often missed. This information helps patients with diabetes tailor their insulin doses, which improves glycemic control and glycated hemoglobin (HbA1c) level. 
  •  While the use of CGM is increasing, its use is rejected by some patients with diabetes on the grounds of cost of device and maintenance, frustration over adherence and lack of accuracy, and issues with new technology usage.



Klemen, Dovc, et al. “On Continuous glucose monitoring use and glucose variability in pre-school children with type 1 diabetes”.  https://doi.org/10.1016/j.diabres.2018.10.005

Oliver, Schnell, et al. “On Role of Continuous Glucose Monitoring in Clinical Trials: Recommendations on Reporting”. doi: 10.1089/dia.2017.0054


Onyi Ibeji, PharmD. Candidate, LECOM School of Pharmacy