Implications of the Hemoglobin Glycation Index on the Diagnosis of Prediabetes and Diabetes

• Published in: The journal of clinical endocrinology and metabolism Vol. 105; no. 3; pp. e130 - e138
• Main Authors: Hsia, Daniel S, Rasouli, Neda, Pittas, Anastassios G, Lary, Christine W, Peters, Anne, Lewis, Michael R, Kashyap, Sangeeta R, Johnson, Karen C, LeBlanc, Erin S, Phillips, Lawrence S, Hempe, James M, Desouza, Cyrus V
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01-03-2020; Copyright Oxford University Press
• Subjects: Administration, Oral; Aged; Blood Glucose - analysis; Blood Glucose - metabolism; Cohort Studies; Diabetes; Diabetes mellitus (non-insulin dependent); Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - diagnosis; Diabetes Mellitus, Type 2 - prevention & control; Diagnosis; Dietary Supplements; Fasting - blood; Female; Glucose; Glucose tolerance; Glucose Tolerance Test; Glycated Hemoglobin A - analysis; Glycosylation; Health Status Indicators; Hemoglobin; Humans; Male; Middle Aged; Observational studies; Online Only; Prediabetic State - blood; Prediabetic State - diagnosis; Prediabetic State - diet therapy; Risk Factors; Variation; Vitamin D; Vitamin D - administration & dosage; Vitamin D - blood; diagnosis; type 2; oral glucose tolerance test; hemoglobin glycation; prediabetes; observational study
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/clinem/dgaa029

Abstract
Objective
Fasting plasma glucose (FPG), 2-hour plasma glucose (2hPG) from a 75-g oral glucose tolerance test (OGTT) and glycated hemoglobin (HbA1c) can lead to different results when diagnosing prediabetes and diabetes. The Hemoglobin Glycation Index (HGI) quantifies the interindividual variation in glycation resulting in discrepancies between FPG and HbA1c. We used data from the Vitamin D and Type 2 Diabetes (D2d) study to calculate HGI, to identify HGI-associated variables, and to determine how HGI affects prediabetes and diabetes diagnosis.
Measurements
A linear regression equation [HbA1c (%) = 0.0164 × FPG (mg/dL) + 4.2] was derived using the screening cohort (n = 6829) and applied to calculate predicted HbA1c. This was subtracted from the observed HbA1c to determine HGI in the baseline cohort with 2hPG data (n = 3945). Baseline variables plus prediabetes and diabetes diagnosis by FPG, HbA1c, and 2hPG were compared among low, moderate, and high HGI subgroups.
Results
The proportion of women and Black/African American individuals increased from low to high HGI subgroups. Mean FPG decreased and mean HbA1c increased from low to high HGI subgroups, consistent with the HGI calculation; however, mean 2hPG was not significantly different among HGI subgroups.
Conclusions
High HGI was associated with Black race and female sex as reported previously. The observation that 2hPG was not different across HGI subgroups suggests that variation in postprandial glucose is not a significant source of population variation in HGI. Exclusive use of HbA1c for diagnosis will classify more Black individuals and women as having prediabetes compared with using FPG or 2hPG.