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. 2021 Apr;23(4):253-258.
doi: 10.1089/dia.2020.0501. Epub 2020 Dec 1.

HbA1c and Glucose Management Indicator Discordance: A Real-World Analysis

Jordan E Perlman  1 , Theodore A Gooley  2 , Bridget McNulty  3 , Jedidiah Meyers  4 , Irl B Hirsch  5
Affiliations

HbA1c and Glucose Management Indicator Discordance: A Real-World Analysis

Jordan E Perlman et al. Diabetes Technol Ther. 2021 Apr.

Abstract

Background: There can be marked discordance between laboratory and estimated (using the glucose management indicator [GMI]) glycated hemoglobin (HbA1c) from continuous glucose monitoring (CGM). This may cause errors in diabetes management. This study evaluates discordance between laboratory and CGM-estimated HbA1c (eA1C). Methods: We performed a retrospective review of patients with diabetes who use CGM. The patients were seen at the University of Washington (UW) Diabetes Care Center from 2012 to 2019. We used UW's Institute of Translational Health Sciences to extract eligible encounters from the electronic medical record. We required that patients use CGM and that HbA1c and sensor data be obtained fewer than 4 weeks apart. There were no exclusion criteria. We calculated HbA1c-GMI discordance for each subject and assessed for any impact of comorbidities. We defined HbA1c-GMI discordance as absolute difference between laboratory and eA1C. Results: This study included 641 separate office encounters. Ninety-one percent of patients had type 1 diabetes. Most patients had diabetes for greater than 20 years. The mean duration of CGM wear was 24.5 ± 8 days. Only 11% of patients had HbA1c-GMI discordance <0.1%, but 50% and 22% had differences ≥0.5% and ≥1%. There was increased discordance with advanced chronic kidney disease (estimated glomerular filtration rate <60). Discussion: We found substantial discordance between laboratory and eA1C in a real-world setting. Clinicians need be aware that HbA1c may not as accurately reflect mean glucose as previously appreciated.

Keywords: Continuous glucose monitoring; Diabetes management; Glucose management indicator; HbA1c.

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Conflict of interest statement

J.E.P.: none; T.A.G.: none; B.M.: none; J.M.: none; I.B.H.: research grants from Medtronic Diabetes and Insulet; consulting with Abbott Diabetes Care, Bigfoot, and Roche.

Figures

FIG. 1.
FIG. 1.
The hashed red line represents the GMI equation. The solid black line is the least-squares regression line fit to the observed data, providing predicted HbA1c for any given CGM mean glucose. CGM, continuous glucose monitoring; GMI, glucose management indicator. Color images are available online.
FIG. 2.
FIG. 2.
The difference between predicted (GMI) and measured HbA1c is shown on the y-axis. The average of the predicted (GMI) and measured HbA1c is given on the x-axis. The bolded line least-squares regression line fit to the observed data.
FIG. 3.
FIG. 3.
The graph is a visual representation of HbA1c discordance calculated by our study as compared to that published in the original GMI article. The percentage of subjects is shown on the y-axis. The HbA1c-GMI discordance is given on the x-axis. Color images are available online.
See this image and copyright information in PMC

References

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