A1c and eAG

Also known as: Hemoglobin A1c; HbA1c; Glycohemoglobin; Glycated hemoglobin; Glycosylated hemoglobin

Formal name: A1c and estimated Average Glucose

The Test Sample

What is being tested?

The A1c test evaluates the average amount of glucose in the blood over the last 2 to 3 months. It does this by measuring the concentration of glycated (also often called glycosylated) hemoglobin A1c. Hemoglobin is an oxygen-transporting protein found inside red blood cells (RBCs). There are several types of normal hemoglobin and many identified hemoglobin variants, but the predominant form – about 95-98% – is hemoglobin A. Hemoglobin A can be further subdivided, with one of the subcomponents known as hemoglobin A1c. As glucose circulates in the blood, some of it spontaneously binds to hemoglobin A. The glucose-hemoglobin molecules formed are said to be glycated. The higher the concentration of glucose in the blood, the more glycated hemoglobin is formed. Once the glucose binds to the hemoglobin, it remains there for the life of the red blood cell - normally about 120 days. The combination of glucose and hemoglobin A is referred to as HbA1c or A1c. A1c is produced on a daily basis and slowly cleared from the blood as older RBCs die and younger RBCs (with non-glycated hemoglobin) take their place.

The way that the A1c is reported is in the process of changing. Traditionally, in the United States, the A1c has been reported as a percentage, and the American Diabetes Association (ADA) has recommended that people with diabetes strive to keep their A1c below 7%. While this is still true, more than a decade of national and international efforts to improve and standardize the A1c test and its reporting led to the release of a consensus statement in 2007 by the ADA, the European Association for the Study of Diabetes, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), and the International Diabetes Federation.

This joint statement and the recent completion of a study called ADAG (A1c-Derived Average Glucose) that further examined the relationship between blood glucose concentrations and A1c have led to a recommendation that A1c be reported worldwide three ways:

as a percentage (based upon National Glycohemoglobin Standardization Program (NGSP) derived units)
in IFCC units (mmol/mol) and
as an estimated Average Glucose (eAG) based upon a formula developed from the ADAG study with either mg/dl or mmol/l as units.

What this means for the diabetic patient and their doctor in the U.S. is that the person’s A1c results will likely be reported both in the percentage that they are used to seeing AND as an eAG, with the same type of values or units (mg/dl) as reported by home glucose monitors and laboratory results.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or a drop of blood is taken from your finger by pricking it with a small, pointed lancet.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.