The era of continuous glucose monitoring and its expanded role in type 2 diabetes

Numerous studies have shown the importance of frequent glucose monitoring for optimal diabetes management1. In clinical practice, various methods are used for glucose monitoring, such as glycated hemoglobin (HbA1c), which reflects the average blood glucose level for the previous 3 months; glycated albumin, reflecting the average blood glucose level for the previous 2 weeks; plasma glucose level in venous blood; and glucose level in capillaries by self-monitoring of blood glucose (SMBG) using a glucometer. Each method has its own strengths and limitations. However, glucose variability, which is also an important predictor of hypoglycemia and diabetic complications, cannot be identified by a single test of HbA1c or plasma glucose level. Information obtained from SMBG is frequently limited due to low patient compliance. Continuous glucose monitoring (CGM) is an innovative technology that helps individuals with diabetes manage their blood glucose levels more effectively. CGM devices work by measuring glucose levels in real-time, and providing the user with alerts and insights that can be used to make informed decisions about their diet, medication and lifestyle. Accordingly, its utility in the management of diabetes patients is growing, and CGM-based metrics (e.g., time in range, coefficient of variation and glucose management indicator) are being introduced2. Recently, guidelines on the use of CGM from professional societies have been updated based on recent clinical trial results (Table 1). In general, guidelines strongly recommend the use of CGM in adults or young type 1 diabetes mellitus patients with multiple daily injections (MDI) or continuous subcutaneous insulin infusion. The American Diabetes Association guidelines recommend that real-time CGM (rtCGM) or intermittent scanned CGM (isCGM) should be offered to adults and youth on MDI or continuous subcutaneous insulin infusion, and also to adults on basal insulin3. The American Association of Clinical Endocrinology also recommends using CGM in individuals on intensive insulin therapy, with problematic hypoglycemia, and pregnant women with intensive insulin therapy4. They also recommend CGM for individuals with type 2 diabetes mellitus being treated with less intensive insulin therapy based on intermediate strength of evidence. The Korean Diabetes Association suggests using rtCGM in type 1 diabetes mellitus patients and type 2 diabetes mellitus patients who require MDI. Adults with type 2 diabetes mellitus receiving treatment other than MDI can periodically use rtCGM for blood glucose control5. Although the level of evidence on using CGM in type 2 diabetes mellitus patients with less intensive therapy than MDI is less strong, it seems that wider applications of CGM are being indicated. The evidence for the use of rtCGM tends to be at a higher level, and for isCGM, there are studies that show it is more beneficial for glucose monitoring than SMBG, but the evidence is still at a lower level than that of rtCGM. A recent study showed that glycemic control and the risk of hypoglycemia improved for up to 24 months when switching from isCGM without an alarm to rtCGM with an alarm6. A randomized controlled trial study was published showing that isCGM with an alarm function is more effective in reducing HbA1c than SMBG in type 1 diabetes mellitus patients7. Previously, hypoglycemic events were fewer in isCGM than SMBG, but evidence for the HbA1c-reducing effect was unclear. This study is meaningful in that it showed the HbA1c-reducing effect by using isCGM. Along with the accumulated experience in using CGM, studies on the benefits of blood glucose control are continuously reported. However, more evidence is needed for type 2 diabetes mellitus patients and individuals on less intensive therapy. Considering the changing trends of glucose monitoring and characteristics of CGM, it can be applied in various situations. In a study comparing isCGM with point-of-care testing for inpatients receiving insulin treatment, patients whose blood glucose was measured with CGM had lower average daily glucose levels and higher detection of hypoglycemia at night and for a long period of time, helping to adjust insulin and reduce the risk of hypoglycemia8. There are several studies showing that CGM captured hypoglycemia more than SMBG, which means that CGM can prevent hypoglycemia better than SMBG9. Also, a randomized controlled trial showed that inpatient use of insulin therapy using rtCGM was safe and effective in reducing hypoglycemia10. It can be expected to reduce morbidity and mortality due to hypoglycemia. Therefore, CGM can be used when type 2 diabetes mellitus patients are hospitalized because of acute situations. Also, CGM can be considered when changing medications, which can cause hypoglycemia, such as sulfonylureas, and when insulin is used for the first time. Pan et al.11 carried out CGM to evaluate glucose variability and a nerve conduction test to evaluate polyneuropathy in type 2 diabetes mellitus patients, and the result showed a positive association between glucose variability and diabetic polyneuropathy. Other studies showed that greater glucose fluctuations were associated with more cardiovascular events, microvascular events and also macrovascular events12. As CGM is very useful for detecting glucose fluctuations, it can be applied in patients with brittle diabetes to improve glucose control, increase time in range and reduce glucose variability. Diabetes patients undergoing surgery, chemotherapy or steroid treatment are likely to experience glucose fluctuations, and studies on the benefit of CGM in these situations are warranted. In addition, in a retrospective observational cohort study, using CGM improved HbA1c and reduced acute complications due to hypoglycemia or hyperglycemia in later-onset type 1 diabetes mellitus and type 2 diabetes mellitus patients13. CGM can be used to prevent not only acute complication, but also long-term complications, and eventually reduce medical costs. As the technology continues to advance, it is likely that CGM devices will become more accessible and integrated into other wearable technologies. This could significantly improve the quality of life for individuals with diabetes, making it easier for them to manage their health and prevent the development of serious complications. Further studies on the appropriate indications of CGM and data analytic tools for better understanding data generated by CGM devices would expand its role in the care of diabetes patients. The authors declare no conflict of interest.