Understanding Your HbA1c

You’ve heard about a diabetes test called a hemoglobin A1C. It’s sometimes shortened to HgbA1c or HbA1c or just A1C. Hopefully, you know what yours is. But do you know what it means and what to do with the information?

Hemoglobin is what makes red blood cells red. It consists of several proteins wrapped around an iron-based molecule called heme. Heme attaches to oxygen and carries it to the cells. That’s why iron is important in our diets. We need iron to make heme to carry oxygen, so our cells can breathe.

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Glucose (sugar) molecules are also floating along in our blood. Glucose attaches itself to all kinds of proteins, including the hemoglobin in red blood cells (RBCs). When glucose levels are high, many more of them will attach.

Hemoglobin coated with glucose is called “glycated” or “glycosylated” hemoglobin. Glycation (“sugar-coating”) may not harm an RBC, but it does tell us if the cell has encountered much glucose during its lifetime. The more glucose has been in the blood, the more RBCs will be glycated. This is what an HbA1c test measures.

A1C isn’t measuring what your blood glucose level is at the moment. It measures how high glucose has been over the last two months or so. RBCs only live about 100–120 days in the bloodstream. Once they become glycated, they stay glycated for life, so the number of glycated RBCs (HbA1c) gives a good picture of how much glucose has been in the blood recently.

The A1C test has several advantages over other tests such as a fasting blood sugar (FBS). You don’t have to fast for an A1C. It can be taken at any time of day. It doesn’t matter what you ate the day before or on the day of the test, because it’s not measuring your current sugar.

Normally, between 4.2% and 5.6% of RBCs will be glycated. The American Diabetes Association considers an A1C between 5.7% and 6.4% “prediabetes.” A level of 6.5% or higher is classed as diabetes.

The higher your A1C, the more extra glucose your cells have been bathing in. More glucose equals more inflammation and more damage to blood vessels. The lower the A1C, the better, at least down to 5.0% or so.

“Average Blood Glucose”
A1C numbers can be hard to understand because they are in percentages. Your regular blood sugar readings are expressed in milligrams per deciliter (mg/dl) with numbers like 94 or 210 or whatever. In Canada and many other countries, sugar readings are expressed in mmol/liter, a number that runs 18 times lower than mg/dl. How do those numbers relate to A1C?

Experts have created a formula for translating an HbA1c level to a number showing the average blood glucose for the previous 8–12 weeks. These Estimated Average Glucose (eAG) numbers are not close to exact, but they give you an idea of how you’re doing.

Your eAG will often be different from the average of your meter readings. People often check at fairly low-sugar times, like in the morning and before meals, and miss the after-meal times when glucose is higher. That is why an A1C or eAG can be surprisingly high and much truer than your finger sticks, because the A1C/eAG includes both high and low times.

An A1C of 5.0 would convert to an average blood glucose of 97 mg/dl (5.4 mmol/l). An A1C of 6.0 yields an average glucose of 126 mg/dl. The range of error is significant. An eAG of 126 could really be anywhere from roughly 100–150. Still, it’s much more informative than a single reading or even a series of them.

More numbers:

A1C: 6.0
eAG (mg/dl USA): 126
eAG (mmol/l Canada/England): 7.0

A1C: 7.0
eAG (mg/dl USA): 154
eAG (mmol/l Canada/England): 8.6

A1C: 8.0
eAG (mg/dl USA): 183
eAG (mmol/l Canada/England): 10.1

A1C: 9.0
eAG (mg/dl USA): 212
eAG (mmol/l Canada/England): 11.8

Note that blood vessel damage is supposed to start at about 140 mg/dl. An A1C of 7.0, which is the ADA’s target number, means your average glucose would be in the danger zone. After-meal spikes would be much higher. It’s a good incentive for trying to get closer to 6.0, if you and your health-care team agree that is reasonable for you.

You can use this calculator to convert your A1C to an average glucose.

Bringing your HbA1c down is the gold standard of all diabetes therapy and self-care. You can use medications, diet, exercise, supplements, and all the self-care measures you see on our site and other diabetes sites.

Because the test looks at a 2–3 month period, better management or a new medicine or herb won’t show up on your A1C for some weeks. That is why fingersticks and glucose monitors are helpful. They show you how what you do affects your sugar now. Those immediate readings will reflect in your A1C after a while.

If A1C and your fingersticks don’t seem to match, it’s probably because you aren’t testing at the right times to catch your highs. Try some after-meal and middle-of-the-night tests to find the problem. A1Cs and glucose checks can work together to show you the way to controlling your diabetes.

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  • JohnC

    Great blog with lots of useful information!
    In the end to avoid complications of diabetes you should know what your blood sugar levels are: before meals, after meals and overnite. If they’re as close to normal as possible, your A1C is going to be great.
    Too bad test strips are so darn expensive – but if you go searching you can find good ones for under $20 a hundred online.