When you were first diagnosed with diabetes, your doctor probably evaluated you with an A1C blood test, also known as hemoglobin A1C, HbA1c, or glycohemoglobin test. This article in Medical News Today explains how this test works, and how it helps to manage blood sugar levels. “Hemoglobin is the protein in red blood cells that transports oxygen around the body. When blood glucose levels are high, some of the glucose binds to hemoglobin. The type of hemoglobin that glucose attaches to is hemoglobin A. The name of the resulting combination is glycated hemoglobin (A1C). Red blood cells live for around 120 days, or 4 months, and at the time of the test, there will be a direct link between the A1C result and the average blood glucose level over the previous 12 weeks or so.”1 [NOTE: This is a direct quote from the referenced source. However, “12 weeks” is not equivalent to “around 120 days, or 4 months.” The rest of the references say “3 months” or “90 days.”]

The A1C test is the primary test used for diabetes management and diabetes research. It measures the attachment of glucose to hemoglobin, the protein in red blood cells that carries oxygen. In the body, red blood cells are constantly forming and dying, but typically they live for about 3 months. Thus, the A1C test is said to reflect the average of a person’s blood glucose levels over the past 3 months. The A1C test result is reported as a percentage. The higher the percentage, the higher a person’s blood glucose levels have been. A non-diabetic normal A1C level is 4.0-5.6%. The HbA1c test is not an average of blood glucose levels. Still, it is logical to assume high glucose level leads to more glycation and increased HbA1c. “Glycosylated hemoglobin: Hemoglobin to which glucose is bound.”2

A1C is not an average of your blood sugar readings over 90 days. It’s all about measuring the damaged (glycated) protein in your red blood cells. The proteins in your red blood cells collect glucose during their 12-week life span. On the days that your blood sugar is low, they collect low levels of glucose. On the days that your blood sugar is high, they collect a higher level of glucose; and more damage to the proteins occurs. It is an indicator of the damage done to all the cells in your body by high blood sugar. “HbA1c test measures the percentage of hemoglobin attached to the glucose in the blood. The glucose level decides the rate of glycation in the blood.”3

Why is this important? It is important because it shows the amount of glucose that is sticking to/damaging/glycating in all your cells in your entire body: arteries and veins (think cardiac disease, impotence), nerve endings (think neuropathy and retinopathy), muscles, organs, everything. It is not an average of blood sugar. It measures the accumulation of cellular damage by blood sugar. Dr. Brian Mowll explains: “A1C is an indicator of damage. Insulin injections do not prevent damage. Besides monitoring long-term glucose control in patients with diabetes, the A1C blood test also helps identify AGE—advanced glycation end products in the body…. While every bit of our bodies is susceptible to this damage, the lining of our blood vessels is particularly sensitive to AGE damage, as well as certain nerve cells like the ones found in our brain, eyes, and kidneys. Even our very DNA is at risk of AGEs moving in and wreaking havoc. AGEs are also responsible for wrinkly, sagging skin, high blood pressure, and most chronic diseases like heart disease, cancer, and stroke. They are also responsible for helping to form the sticky amyloid proteins and neurofibril tangles that destroy the brains of those people with Alzheimer’s and dementia.”4

To guide you in setting your own goals/objectives for your A1C, here’s information from the CDC:

Chart of Normal and Elevated HbA1c Levels:5

  • Normal – Below 5.7%
  • Pre-diabetes – 5.7% to 6.4%
  • Diabetes – 6.5% or greater

For more detail, please refer to this Composite A1C Chart. (Click image to open in a new tab where it can be enlarged.)

*I have not been able to find any resource that tells me which convention is correct: A1C (with an upper case “C”) or A1c (with a lower case “c”). All resources say that A1C, A1c, and HbA1c stand for “Glycated Hemoglobin” [not an acronym – just means “average blood glucose control over 2-3 months”]. I have checked presumably professional websites, such as WebMD, Mayo Clinic, and American Diabetes Association. I have checked books specifically on diabetes from recommended authors. Some use “A1C” and some use “A1c” and there does not seem to be any pattern. So, for purposes of consistency in this website, I have decided to go with the CDC usage: “The A1C test—also known as the hemoglobin A1C or HbA1c test…”6 which seems to infer that the abbreviation for “hemoglobin A1C” is correctly written as “HbA1c” but otherwise can be abbreviated as “A1C.”


1MacGill, Markus; medically reviewed by Deborah Weatherspoon, PhD, RN, CRNA. “Everything you need to know about the A1C test,” Medical News Today (March 27, 2019). https://www.medicalnewstoday.com/articles/265443.php (accessed on 7/30/2020).

2Shiel, William C., Jr., MD, FACP, FACR. “Medical Definition of Glycosylated hemoglobin,” MedicineNet, n.d. https://www.medicinenet.com/script/main/art.asp?articlekey=16295 (accessed on 7/30/2020).

3Thiruvelan. “What is Glycation of Hemoglobin HbA1c?” Healthy-ojas (June 23, 2010). http://healthy-ojas.com/diabetes/A1C.html (accessed on 7/30/2020).

4Mowll, Dr. Brian. “Why The Hemoglobin A1C Test Is So Important,” The Diabetes Coach, DrMowll (March 28, 2018). https://drmowll.com/why-the-hemoglobin-A1C-test-is-so-importnat/ (accessed on 7/30/2020).

5Stöppler, Melissa Conrad, MD; medical editor William C. Shiel, Jr., MD, FACP, FACR. “Hemoglobin A1C Test (HbA1c),” eMedicine Health (November 27, 2019). https://www.emedicinehealth.com/hemoglobin_A1C_HbA1c/article_em.htm#facts_and_definition_of_hemoglobin_A1C_HbA1c (accessed on 7/30/2020).

6“All About Your A1C,” Centers for Disease Control and Prevention, n.d. https://www.cdc.gov/diabetes/managing/managing-blood-sugar/a1c.html (accessed on 12/6/2020).

Additional References

The A1C Test & Diabetes

What is Glycation of Hemoglobin HbA1C?

Why the A1C Test Is Important