Using the HbA1c Test to Monitor Diabetes

Over the years, several methods have been developed that enable those with diabetes to regularly monitor their condition for purposes of improved control. One such method was developed through the study of the process of oxygen transport in the blood stream by means of hemoglobin. Hemoglobin is found in the red blood cells (RBC) and is responsible for carrying oxygen to the tissues; it also is what makes blood appear bright red.

What is Hemoglobin?

Hemoglobin is a component of the red blood cells (RBC). Its major constituents consist of the protein called globin and the iron-containing pigment called hemo. Structurally, hemoglobin is quite complicated. It is comprised of polypeptides (4 lengthy chains of protein). Two alpha (α) chains and two (β) chains.[1]

Hemoglobin is also noted as an iron carrying porphyrin compound. Simply put, this molecule is a transport molecule. It takes up oxygen in the lungs. It then releases it to all the cell tissues in the body.[2] During the process, it absorbs or picks up certain substances from the blood stream. If glucose is present in high amounts in the bloodstream, hemoglobin will pick up a lot of these sugars.[3]  Glucose binds or “glycosylates” with the RBC’s hemoglobin. During this process, it becomes altered, and the hemoglobin coated with sugar is said to be glycated. When this occurs, it is designated as A1c or HbA1c.

Using Hemoglobin to measure Blood Glucose

HbA1c can be used as a measure of the glucose in the blood stream, and diabetics are very familiar with the test. Normal levels are bewteen 4.0% to 5.7%. In a diabetic, however, the levels are much higher. They range from between 6% to 15%, with anything over 6.5% being diagnostic for diabetes.[4] Knowing the levels of glucose in your system is essential to controlling diabetes. Unlike standard blood tests where the measurements show only the immediate picture, the HbA1c delivers a concise depiction of the levels for the past 2-3 months. As a result, the standard blood tests and the HbA1c tests used to detect glucose levels complement each other.

Terminology and Understanding its Value

In clinical practice a number of terms are employed. The A1c hemoglobin may be referred to as

  • Glycosylated hemoglobin
  • Glycohemoglobin
  • HbA1C
  • HgbA1C

Although the most common term is HbA1c, all terms refer to the interaction between hemoglobin and glucose. Whatever term is used, the expression of test values is stated as a percentage of hemoglobin that is glycated. Unfortunately, whatever the A1c number is, it does not directly match the average blood glucose level. In order to convert the values, a factor has to be applied. A table is available on the internet to make the conversion easy. For instance, an A1c of 7.0% is equal to an average fasting glucose level of 150. When in doubt, don’t hesitate to ask your doctor or other medical professional about the test results, or you can contact a diabetes association or group.

A new method of expressing the average blood glucose is the estimated average glucose (eAG). The eAG is stated in mg/dl units, instead of a percentage, which are the same units the glucose meters use. The HbA1C percentage can be converted to the eAG mg/dl units also.

Whatever monitoring test is used, you need to make sure it is performed in a certified laboratory or that you purchase a quality home monitoring kit from a reliable source. There is a “home test” for HvA1c to make results available faster than a lab.


When you should take an A1c test depends, to a large extent, upon your ability to maintain control of your diabetes. Generally, it is recommended you have the test done two times a year.[5] This schedule can change if you alter your medical therapy or you have failed to meet your treatment goals. It will not, however, be used more frequently than every 2 months unless special circumstances exist.

Controversies Concerning A1C

The target level for the HbA1c value is currently under debate. Some organizations believe generally that 6.5% is a good target. Others support a figure of 7% believing 6.5% indicates someone is already too close to possibly developing hypoglycemia. In fact, several large studies showed that aggressive glucose control with a goal A1c of <6.0% actually increased the mortality rate signifcantly. As a result, most doctors will aim for a goal of <7.0%. There are other issues concerning the use of HbA1c. While the test may be easily affordable in North America, it is not inexpensive. It’s been noted by a physician that the HbA1c measurement test is actually 3 times more expensive than other monitoring tests. There is also concern that using a higher percentage value will result in the identification of fewer patients.

The HvA1c does indicate how well the blood sugar is being controlled. It can help to motivate an individual to make lifestyle changes or verify that current treatment methods are successful.

Remember though that no test is free from problems. The tests conclusions are based on a particular type and range of hemoglobin. They may not turn out to be either appropriate or applicable if there is some form of a blood related disease present such as anemia, blood loss or sickle cell disease.


The HbA1c test is part of your arsenal for managing diabetes. It helps you see when you are on the right path to controlling the disease. When the numbers are good and do not go up and down like a yo-yo, it gives you a morale boost and puts an end to the doubts about your ability to be in control. Understanding what the tests mean, what they do and how they can help you take charge of your diabetes is a significant step in your ability to master your life.


[1] Murray, R.K;  Bender, DA; Botham, KM; Kennelly, PJ; Rodwell, VW; and Weil, PA (2009). Harper’s Illustrated Biochemistry 28th ed. New York: Lange McGraw Hill.

[2] Marcovitch, H (2006). Black’s Medical Dictionary 41st edition. Lantham, Maryland: Scarecrow Press.

[3] American Diabetes Association (2009). Type 2 Diabetes. Your Healthy Living Guide. Alexandria, VA: ADA.

[4] Burant, CF (2008). Medical Management of Type 2 Diabetes, 6th edn. Alexandria, VA: ADA.

[5] Stanley, K (2009). 50 Things You Need To Know About Diabetes. Alexandria, VA: ADA.

6 Davies, PH; Chellamuthu, P; and Patel, V (2010).  “How to Diagnose Diabetes? Practicalities and Comments on the WHO Provisional Recommendation in Favour of Hba1c.”  British Journal of Diabetes & Vascular Disease, 10: 261.

This article was originally published July 12, 2012 and last revision and update of it was 9/10/2015.