Associations between HbA1c-derived estimated average glucose and fasting plasma glucose in patients with normal and abnormal hemoglobin patterns

Abstract

Fasting plasma glucose (FPG) and HbA1c are well-known tests for monitoring short and long-term glycemic control, respectively. Estimated average glucose (eAG) is derived from the HbA1c for expression in the same units as FPG. The present study aimed to evaluate the association between eAG and FPG values. This retrospective study was performed on 1285 patients who measured the FPG and HbA1c (capillary electrophoresis method) values on the same day. They were initially divided into 3 hemoglobin-pattern groups, normal, HbE, and high HbA₂, and then these 3 groups were further subdivided into whole group, subgroup 1 (HbA1c ≤ 7%) and subgroup 2 (HbA1c >7%) for analytical comparisons. The eAG values were calculated using Nathan’s equation. The differences, agreements, and correlations between eAG and FPG were evaluated. Good agreements and strong positive correlations between eAG and FPG values were observed in all 3 whole groups. In subgroup analysis, the degrees of agreement and correlation depended on the level of glycemic control, as all associations became stronger with better glycemic control. Additionally, the HbA1c levels and different eAG-FPG values between the normal and other groups were not significantly different in either whole group or subgroup comparisons. Our study found good agreements and strong positive correlations between eAG and FPG in all groups, indicating that high HbA₂ or HbE did not affect the HbA1c levels or thus the associations between eAG and FPG. Reporting the eAG together with the HbA1c value should help improve the understanding of glycemic status in patients, leading to improved blood glucose control.

Keywords:

• Estimated average glucose
• HbA1c
• Hemoglobin pattern
• fasting plasma glucose
• diabetes mellitus

Acknowledgments

We thank Mr. Dave Patterson of the International Affairs Office, Faculty of Medicine, Prince of Songkla University for editing the manuscript. Additionally, we thank Meditop Co., Ltd. for providing information on hemoglobin patterns.

Author contributions

Wilaiwan Sriwimol was the principal investigator, conceived and designed the study, performed data collection and curation, analyzed data, and was responsible for drafting and editing the manuscript. Phattanapong Choosongsang designed the study, performed data collection, analyzed data, and drafted the manuscript. Pensiri Choosongsang designed the study, performed data collection and edited the manuscript. Warakorn Petkliang and Pittaya Treerut performed data collection. All authors reviewed and approved the final version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).