Back to Basics: What is Hemoglobin A1C (HbA1c)?

A high A1C is often the lab result that leads to a diagnosis of diabetes. It is also a term that is discussed regularly at diabetes appointments. In conversations with clients, I often find they have not been provided with a good understanding of what A1C is exactly and why it matters.

This article explains:

What is Hemoglobin A1C | Beyond Diabetes Nutrition - Lucy Zhang, Registered Dietitian

What is Hemoglobin A1C (HbA1c)?

HbA1c, also referred to as hemoglobin A1c, or just A1C, is glycated hemoglobin. It is a blood test measuring the percentage of hemoglobin proteins in your blood that have glucose (sugar) attached. An A1C test reflects your average blood sugar for the past 2 to 3 months (though it is weighted more heavily towards your most recent month).

Hemoglobin is a protein in red blood cells responsible for transporting oxygen in your body. Each red blood cell contains about 270 million hemoglobin molecules. When there is a higher concentration of sugar in your blood, such as in diabetes, more sugar molecules attach to the hemoglobin of your red blood cells. This attachment process is called glycation - thus, “glycated” hemoglobin.

Once sugar attaches to hemoglobin, it stays attached for the lifespan of the red blood cell, which averages about three to four months. This is why A1C is often checked once every 3 months. For people with stable A1C that trends within target, your doctor may monitor A1C every 6 months. Alternatively, if a treatment change has been made, your doctor may choose to recheck A1C sooner.

A1C reflects average blood glucose (sugar) over the past 2 to 3 months | Beyond Diabetes Nutrition - Lucy Zhang, Registered Dietitian

What does your A1C result mean?

A1C is one of the blood tests used in diagnosing diabetes and monitoring blood sugar control. It can be measured at any time during the day since it measures long-term blood sugar control rather than what blood sugar is at a particular moment in time. In Canada, A1C levels of 6.5% or higher suggest diabetes, while an A1C of 6.0 - 6.4% suggests prediabetes (high risk of developing diabetes and its complications).

Keep in mind that during diagnosis, your doctor will look at A1C along with other blood tests such as random blood glucose, fasting blood glucose, as well as any symptoms you may be experiencing.

What does your a1c result mean  | Beyond Diabetes Nutrition - Lucy Zhang, Registered Dietitian

Why does A1C matter?

A1C is an important predictor of diabetes-related complications. The UK Prospective Diabetes Study (UKPDS) (a landmark study in diabetes research) showed that for people with type 2 diabetes - improving A1C by 1% (meaning a 1% decrease in A1C) lowers the risk of microvascular complications by 37%.

Microvascular complications include:

  • Retinopathy (damage to the retina of the eyes)

  • Neuropathy (damage to nerves)

  • Nephropathy (damage to the kidneys)

1% decrease in a1c equals 37% decrease in risk of microvascular complications  | Beyond Diabetes Nutrition - Lucy Zhang, Registered Dietitian

What should my A1C goal be?

For most adults with type 1 or type 2 diabetes, the A1C goal is 7.0% or lower. A1C levels above 7% are associated with a large increased risk for microvascular and cardiovascular (heart and blood vessel) complications. If you can reach lower A1C levels without episodes of hypoglycemia (low blood sugar), a target A1C of 6.5% or lower may be appropriate to further lower the risk of retinopathy and nephropathy.

Keep in mind, everyone is different, and there are other factors that affect A1C levels. Your doctor may give you an individual A1C goal that takes into account your overall health.

How does A1C differ from blood glucose (sugar)?

While A1C paints a good picture of average blood sugar, an A1C of 7% does not equal an average blood sugar of 7 mmol/L. This can be confusing at times!

You’ll notice that while A1C is reported as a percentage (%), blood glucose (blood sugar) is measured in mmol/L (whether it’s lab testing blood sugar or your at-home glucometer). An A1C of 7% actually equals an average blood sugar of about 8.5 mmol/L.

To convert your A1C to estimated average blood sugar, use the following equation:

Average Blood Sugar (mmol/L) = A1C (%) x 1.59 - 2.59

Or refer to this figure for a quick estimate:


Canadian Diabetes Association. Building Competency in Diabetes Education: The Essentials (5th Ed.) Toronto: Canadian Diabetes Association. 2019.

Imran S, Agarwal G, Bajaj HS, Ross S. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Targets for Glycemic Control . Can J Diabetes. 2018;42:S42-S46.

Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ. Translating the A1C Assay into Estimated Average Glucose Values. Diabetes Care. 2008;31:1473–1478.

Punthakee Z, Goldenberg R, Katz P. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Definition, Classification and Diagnosis of Diabetes, Prediabetes and Metabolic Syndrome . Can J Diabetes. 2018;42:S10-S15.