Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring

Abstract

While A1C is well established as an important risk marker for diabetes complications, with the increasing use of continuous glucose monitoring (CGM) to help facilitate safe and effective diabetes management, it is important to understand how CGM metrics, such as mean glucose, and A1C correlate. Estimated A1C (eA1C) is a measure converting the mean glucose from CGM or self-monitored blood glucose readings, using a formula derived from glucose readings from a population of individuals, into an estimate of a simultaneously measured laboratory A1C. Many patients and clinicians find the eA1C to be a helpful educational tool, but others are often confused or even frustrated if the eA1C and laboratory-measured A1C do not agree. In the U.S., the Food and Drug Administration determined that the nomenclature of eA1C needed to change. This led the authors to work toward a multipart solution to facilitate the retention of such a metric, which includes renaming the eA1C the glucose management indicator (GMI) and generating a new formula for converting CGM-derived mean glucose to GMI based on recent clinical trials using the most accurate CGM systems available. The final aspect of ensuring a smooth transition from the old eA1C to the new GMI is providing new CGM analyses and explanations to further understand how to interpret GMI and use it most effectively in clinical practice. This Perspective will address why a new name for eA1C was needed, why GMI was selected as the new name, how GMI is calculated, and how to understand and explain GMI if one chooses to use GMI as a tool in diabetes education or management.

Impact of mismatches in HbA1c vs glucose values on the diagnostic classification of diabetes and prediabetes

“…The patterns were generally similar with definition of average glucose as OGTT fasting glucose alone [as used by Hempe et al [3] in their analysis of data from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial], and as the mean of OGTT fasting glucose and OGTT 2-h glucose (Table S2). With all three definitions of average glucose, the regressions for the OGTT diabetes group in the present study [early in their natural history, with mean HbA 1c of 44 mmol/mol (6.2%) and diabetes which was previously unrecognized] had a slope that was less steep than the slope of the regression found in the A 1c -Derived Average Glucose (ADAG) study [4] and the slopes observed in patients with diabetes who were later in their natural history and who had higher mean HbA 1c [10,11]. Within each normal, prediabetes and diabetes OGTT group, participants were divided into mismatch tertiles of HGI, as low, intermediate and high, then each tertile was combined across the OGTT groups (e.g.…”

“…Regressions of HbA 1c levels (mmol/mol) vs average glucose (AG) levels (mmol/L),for all participants and glycemic status groups, based on oral glucose tolerance test (OGTT) glucose levelsnormal glucose metabolism (normal), prediabetes, and diabetes, defined as in Methodsand with average glucose defined as OGTT fasting glucose alone, the mean of OGTT fasting glucose and OGTT 2-h glucose, and the mean of OGTT fasting glucose, OGTT 2-h glucose, and GCT 1-h glucose levels. Also included for comparison are regressions from the A 1c -Derived Average Glucose (ADAG) study (including both diabetes and nondiabetes, and average glucose based on CGM and SMBG) [5]) and those recently reported by Beck et al [11] and Bergenstal et al [12] [including only diabetes, and average glucose based on CGM]; the participants with diabetes in these three studies were later in their natural histories, with higher HbA 1c levels, compared to those with previously unrecognized diabetes in the present study. Table S3.…”

Beyond HbA1c: using continuous glucose monitoring metrics to enhance interpretation of treatment effect and improve clinical decision‐making

“…Historically, this has been represented by an average glucose, which in theory could be converted to an estimated HbA 1c . However, this is not exactly accurate and has led to a call to consider a new metric: glucose management indicator (GMI) [14]. The GMI is proposed as a new indicator for clinical reports such as the ambulatory glucose profile that rephrases the CGM data to a similar and correlated number for HbA 1c but avoids the troublesome lexicon of estimated HbA 1c , which should be used carefully and only in the context of formulas designed to produce estimates of real HbA 1c values, not derivatives of average blood glucose [15].…”

Chinese clinical guidelines for continuous glucose monitoring (2018 edition)

“…Using a standard formula, a value called “estimated HbA 1c ” was generated from the mean glucose, and the term was later replaced by “glucose management indicator” (GMI). Many patients and clinicians find the GMI to be a helpful educational tool in understanding the CGM‐generated glucose profiles and will facilitate optimal diabetes management and the adjustment of anti‐diabetic therapy …”