Continuous Glucose Monitoring for Prediabetes: What Are the Best Metrics?

Abstract

Background: Continuous glucose monitoring (CGM) has transformed the care of type 1 and type 2 diabetes, and there is potential for CGM to also become influential in prediabetes identification and management. However, to date, we do not have any consensus guidelines or high-quality evidence to guide CGM goals and metrics for use in prediabetes.

Methods: We searched PubMed for all English-language articles on CGM use in nonpregnant adults with prediabetes published by November 1, 2023. We excluded any articles that included subjects with type 1 diabetes or who were known to be at risk for type 1 diabetes due to positive islet autoantibodies.

Results: Based on the limited data available, we suggest possible CGM metrics to be used for individuals with prediabetes. We also explore the role that glycemic variability (GV) plays in the transition from normoglycemia to prediabetes.

Conclusions: Glycemic variability indices beyond the standard deviation and coefficient of variation are emerging as prominent identifiers of early dysglycemia. One GV index in particular, the mean amplitude of glycemic excursion (MAGE), may play a key future role in CGM metrics for prediabetes and is highlighted in this review.

Keywords: continuous glucose monitoring; glucose intolerance; glycemic variability; impaired glucose; metrics; prediabetes.

Figure 1.

An illustration of the concordance (overlapping sections) and discordance (sections without overlap) in A1c, OGTT, and FPG in diagnosing prediabetes. This is a conceptual illustration only and the size of overlapping sections is not proportional to rates of inter-test concordance.

Figure 2.

Consensus recommendations for time in range, time above range and time below range for different patient populations (a) adults with type 1 or type 2 diabetes; (b) older adults and/or adults with type 1 or type 2 diabetes at higher risk of hypoglycemia due to age, duration of diabetes, duration of insulin therapy and/or hypoglycemia unawareness; (c) children and adolescents; (d) pregnant women with type 1 diabetes, based on limited evidence; and (e) pregnant women with gestational or type 2 diabetes, but no consensus recommendations available. This figure was reproduced from the work of Bellido et al Reprinted with permission.

Figure 3.

A summary of studies from 2007 to 2022 that examined normoglycemia on CGM. This figure was reproduced from the work of Klonoff et al Reprinted with permission.

Figure 4.

Illustration of CGM profiles in states of normoglycemia and prediabetes. (a) Example of a CGM profile in a healthy 41-year-old man with an A1c of 5.5%. The average overnight glucose is within the normal range, close to 100 mg/dl. Minor glycemic spikes occur after meals, but most postmeal excursions remain < 140 mg/dl with a duration of < 30 minutes. (b) Two illustrations of possible CGM profiles in prediabetes. Prediabetes may be characterized by elevated overnight glucose, sharp postmeal glucose spikes, increased duration of postprandial hyperglycemia, increased frequency of hyperglycemia over 24 hours or a combination of any of these profiles. (b1) The average glucose overnight is high, close to 150 mg/dl. Moderate glucose spikes occur after meals. Post-meal glucose excursions persist for hours. (b2) The average glucose overnight is near normal. More severe glucose spikes occur after meals. Postmeal glucose excursions have variable durations but can persist up to hours. (c) Hypothetical illustration, represented by the light blue horizontal lines, of the probable normal range of glucose levels in people without diabetes that could serve as the target range for prediabetes.