Your A1C is a three month average, not a report card

The result lands in the portal, or gets read out to you over the phone in a voice that gives nothing away. One number, one decimal place.

Whatever it says, most people hear it as a verdict on how they have been doing. A good number means you were good. A higher one means you were not.

That is not what the number is, and knowing what it actually measures changes what you do with it.

What the test is measuring

Sugar in your blood attaches to hemoglobin, the protein inside red blood cells that carries oxygen. The more sugar there has been in your blood, the more of your hemoglobin is carrying some. The A1C measures what proportion is carrying it, which is why the result is a percentage.

Red blood cells live around three months before they are replaced, so the test cannot help but be an average over roughly that period. It is not a measure of today, and it is not affected by whether you ate before the blood draw, which is why you do not need to fast for it. The average is weighted: the most recent few weeks count for more than the oldest ones.

A1C answers one question well: what the average has been. It cannot tell you what the days looked like.

Why it lags what you did last week

If you changed something a month ago, started walking after supper, cut back on the evening snacking, began a new medication, the next A1C shows only part of it. The rest of the window is still full of the weeks before you changed anything.

This is the most common reason people feel discouraged by a result. They did the work, the number barely moved, and the conclusion they draw is that the work does not matter.

The honest version is that three good weeks inside a three month average is three good weeks inside a three month average. It shows up as a small change now and a larger one on the next test. If your day to day readings have improved, that improvement is real, and the A1C is simply the slowest place to see it. The reverse holds too: a rough couple of months does not vanish because the last fortnight went well.

What the number cannot see

An average has no shape. Two people can walk out with exactly the same A1C and have had entirely different three months.

One of them has been steady, most readings in a narrow band, no drama. The other has been swinging between lows in the afternoon and highs overnight, and the two cancel out into a respectable-looking average. The second person is not doing well, and their A1C does not say so.

That is why an A1C is never read on its own. Your meter readings, or the time in range from a sensor if you use one, describe the shape. Lows in particular are invisible to an A1C, and they are the thing your care team most wants to hear about.

Targets are individual, and a higher one is not a lower standard

Diabetes Canada’s clinical practice guidelines set an A1C of 7.0% or less as the target for most adults with type 2 diabetes. The same guidelines say a higher target is appropriate for some people: those who are older or frail, those with limited life expectancy, and those who have had severe low blood sugar or no longer get warning symptoms before a low. For some people a tighter target is considered, where it can be reached safely, to further reduce the risk of eye and kidney damage.

The right number for you is a clinical decision that takes in your age, your other conditions, your medications and how you respond to them. If your target differs from someone else’s in your family, that is not because less is expected of you. Chasing a low number with medication that causes dangerous lows is a worse outcome than a slightly higher one.

Ask what your target is and why it is that. There is a real answer.

When the A1C is not telling the truth

The test assumes your red blood cells behave normally. When they do not, the result can read falsely high or falsely low, and the number stops meaning what it usually means.

Things that can do this include iron deficiency and other anemias, recent blood loss or a transfusion, chronic kidney disease, dialysis, pregnancy, and inherited hemoglobin variants such as sickle cell trait or thalassemia trait, which are more common in people with African, Mediterranean, Middle Eastern, South Asian or Southeast Asian ancestry.

If any of those apply to you, say so. Your care team can lean on other measures, such as your own readings, sensor data or a fructosamine test, rather than on an A1C that is quietly wrong.

Worth a word with your care team

• Any low blood sugar, whether or not you needed help with it. Lows do not appear in an A1C, and they change what your target should be.
• Thirst, urinating often, blurred vision, unexplained weight loss, unusual tiredness, or infections that keep returning. These say something about now, not about the last three months.
• An A1C that has climbed across two or three tests in a row, even if each rise looked small.
• A result that does not match how you feel or what your meter shows. That gap is information, and sometimes it points at one of the conditions above.
• A medication you have not been taking, for any reason, including cost. Nobody needs a speech. Cost is one of the most fixable causes of a rising A1C, and your care team can only work with what they know.

One thing to be plain about: do not change, stop or increase a medication because of an A1C result. Dose changes belong to the person who prescribes it, and they are working from more than this one number.

One small place to start

Before your next appointment, find your last three A1C results and their dates. Most portals show them together, and if not, you can ask.

Look at the direction rather than the last value. Then bring one question: what is my target, and what would we change if the next one looks like this one? That question turns a percentage into a plan.

If you are a 360Care member and a result has landed that you do not know how to read, message your care team in the app. Bring the number and roughly what the three months behind it looked like. That second part is the half nobody asks for, and it is usually where the useful conversation is.