Clinical Use of Professional Continuous Glucose Monitoring

The costs of managing diabetes are growing at an unsustainable rate. According to the ADA website, the cost (direct and indirect) in 2012 was $245 billion and continues to grow. As clinicians, we fully appreciate that lowering the A1c is one of the keys to lowering the costs associated with diabetes complications. It has been estimated that lowering the A1c across all patients with diabetes by 1% could lower the cost of care by $55 billion annually. It is also well established that intensive diabetes management to lower the A1c is accompanied by the increased risks associated with glycemic variability. Indeed, emergency room visits for hypoglycemia in 2011 were *282,000 with an estimated $1.2 billion in hospitalization costs. There is abundant evidence that a necessary intervention to prevent and reduce glycemic variability is the inclusion of glucose monitoring in the treatment plan, with optimization of patient engagement in this process. The current state of glucose monitoring includes the use of A1c, self-monitoring of blood glucose (SMBG), and continuous glucose monitoring (CGM), each with its own strengths and limitations. The A1c reigns as the current standard of care and represents the average glucose over approximately a 12-week period. As an average, it has limitations in detecting hypoglycemia and glycemic variability. An example is that an average glucose of 154 mg/dL can be achieved by blood glucose levels fluctuating between 120 and 188 mg/dL, whereas a similar average glucose of 154 mg/dL can be achieved by blood glucose levels fluctuating between 50 and 258 mg/dL. Both glycemic patterns would be approximated by an A1c of 7.0% but reflecting very different treatment responses. The SMBG provides information only for points in time and is limited by the frequency of testing and the accuracy of reporting. Overnight data are very difficult to obtain and hypoglycemic episodes are often missed. SMBG is also limited by the accuracy of reporting. Langer and Mazze reported that among 34 patients with gestational diabetes who were instructed to do and record SMBG four times daily for 2 weeks, 33 (97%) omitted from their logbooks values that were recorded in their meter memory. Professional CGM provides a significant amount of glucose data over time that can be useful in informing therapeutic decisions for the clinician and patients. Professional CGM with the ambulatory glucose profile (AGP) has the ability to translate large amounts of glucose data into clinically relevant, useful, and actionable information. However, professional CGM has not been widely adopted in type 2 diabetes mellitus (DM) in large part because of reimbursement issues, high startup costs, and nonstandardized reporting of glycemic data and patterns. We have seen from previous studies that glucose dynamics and glycemic variability may contribute to the progression of microand macrovascular disease in individuals with DM. An illustrative example for macrovascular disease has been shown between glycemic variability and carotid intima media thickening.7,8 It is postulated that glycemic variability causes an overproduction of potentially harmful reactive oxygen species and increases oxidative stress resulting in worsened endothelial function. Evidence also exists for glycemic variability as a strong predictor of hypoglycemia and poor glycemic control, irrespective of the baseline A1c. These observations make a compelling argument for the importance of glycemic variability and for minimizing it as a key treatment goal, irrespective of the form of diabetes. The A1c is still considered the gold standard indicator of glycemic control in diabetes management in large part because of its demonstrated correlation with microvascular complications. However, the A1c represents the average blood glucose over 8 to 12 weeks and cannot characterize glucose fluctuations during the day or glycemic variability. Although beyond the scope of this report, there are other influences that can affect the A1c in ways that make this metric less reflective of true blood sugar levels over time, such as hematocrit, hemoglobinopathies, or concomitant use of certain medications, to name a few. Thus, for many reasons,