Relationship between A1C and fasting plasma glucose in dysglycemia or type 2 diabetes: an analysis of baseline data from the ORIGIN trial

Abstract

Objective: A1C measurement has advantages over measures of plasma glucose. Few studies have evaluated the A1C-fasting plasma glucose (FPG) relationship and whether oral antidiabetes drugs (OADs) and ethnic or geographic variations affect the relationship. Baseline A1C and FPG data from the Outcome Reduction with Initial Glargine Intervention (ORIGIN) trial participants were analyzed to 1) elucidate the relationship between A1C and FPG in people with moderate dysglycemia (A1C 5.6-9.0% [38-75 mmol/mol]) and additional risk factors for cardiovascular disease, 2) determine whether this relationship is altered by use of an OAD, and 3) study whether geographic and ethnic differences exist.

Research design and methods: Analysis was performed of 12,527 participants with dysglycemia or early type 2 diabetes recruited in North America, South America, Europe, Australia, and Asia who comprised white, Latin American, Asian, black, and other ethnicities. The A1C-FPG relationships were analyzed using cubic B spline curves in all participants and in subgroups not using an OAD or using an OAD and comprising persons of different ethnic or geographic origin.

Results: A strong relationship between FPG in the range of 5.6-9.0 mmol/L and the corresponding A1C was seen across different geographic regions and ethnic groups. A smaller increase in A1C per unit increase in FPG occurred for persons taking an OAD versus those not taking an OAD.

Conclusions: The strong relationship between A1C and FPG in moderate dysglycemia is not significantly affected by ethnic or geographic differences. Use of an OAD alters the relationship and should be considered when interpreting A1C level.

Trial registration: ClinicalTrials.gov NCT00069784.

Figure 1

Spline curves with 95% CIs of the relationship between FPG and A1C are shown for the total group (A), persons on an OAD (B), persons not on an OAD (C), and persons on metformin (D), a sulfonylurea (E), or any other OAD (F). (A high-quality color representation of this figure is available in the online issue.)

Figure 2

The difference in estimated A1C (%) between the groups on an OAD versus the group not on an OAD at FPG values ≥5.6 mmol/L. Differences were derived from the respective spline curves.

Figure 3

Spline curves with 95% CIs of the relationship between FPG and A1C are shown for persons from different geographical regions not on an OAD (A) and on an OAD (B). (A high-quality color representation of this figure is available in the online issue.)