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Diabetes Simplified: A1C Testing

The science (or black magic) behind A1C testing.


By Wil Dubois

“Mirror, mirror, on the wall, who’s the best-controlled of all?”

What the Wicked Queen would have asked if she’d had diabetes instead of vanity issues

If you’ve had diabetes for any time at all, you’ve probably heard of the A1C test. Sometimes, it’s also called the HbA1c test, the Hemoglobin A1c test, or the glycated hemoglobin test. They’re all the same thing. This is a lab test that allows your doctor, by consulting with a magic mirror, to determine how well your diabetes has been controlled, night and day, for the last three months.

If that’s not black magic, I don’t know what is.

Of course, as sci-fi writer Arthur C. Clarke famously said, “Any sufficiently advanced technology is indistinguishable from magic.”

The A1C has become the widely accepted benchmark for diabetes control. It’s used to classify who is in control and who is not, and to quantify risk levels of those not in-target. The higher the A1C, the greater the risk of complications. The A1C is now also used diagnostically, with A1C scores actually used to diagnose new-onset diabetes.

How Does It Work?

Well, like I said, it’s magic: in this case, the magic of biochemistry. The test measures the average blood sugar level for the past three months. It can do this because glucose sticks to red blood cells, just like powdered sugar sticks to freshly-fried doughnut holes. The result of the test is expressed as a percentage: 6.2 percent…7.8 percent…8.3 percent…9.6 percent…12.4 percent…and so on. Most A1C scores are only expressed in 10ths of a percent, but some labs report 20ths, as well, so you might see an A1C of 6.79 percent or 8.32 percent.

Wait a sec. A percentage of what, exactly?

The percentage of hemoglobin in the sample of red blood cells that has glycated (I told you it was magic.) Or, in plain English, the amount of powdered sugar that has stuck to the doughnut hole.

The key to the test’s success is the fact that you can’t scrape sugar off the red blood cells, no matter what you do—so the cells essentially maintain a “chemical memory” of the levels of glucose they’ve been swimming in. In fact, a typical red blood cell only lives for 90 days. No A1C test can show what the sugar was like earlier than 90 days ago, because there are no red blood cells left in your body from that time.

Why Do We Take the Test?

We run the A1C because meters, unlike the magic mirror, lie. Well, that’s not really true. Meters don’t lie so much as mislead. They mislead because we can rarely get enough test strips for them, and even if we could, it’s impossible to test at all times of the night and day with a meter. We rely on the A1C to give us a snapshot of the big picture. The test averages all the highs and lows, the bright spots and dark corners. The days and the nights. The weekdays and the weekends.

You know, if you only tested your blood sugar with a meter first thing in the morning, you could easily mislead yourself about how good your diabetes control is. For most dFolks, first thing in the morning is low tide. It’s the time when blood sugar is at its lowest. If you then eat oatmeal, toast, and dates, your blood sugar might soar upwards, and stay high for hours—perhaps all day—not dropping again until the middle of the night.

The once-a-day in the morning test is missing the real action: the fact that you are high half the time. That’s the magical beauty of the A1C—it can’t be so easily fooled. It peeks behind the curtain to see what’s really happening. But that doesn’t mean that testing with a meter is a waste of time—far from it. Read on.

What the A1C Tells Us, and What It Doesn’t Tell Us

While the A1C tells an important story, it doesn’t tell the whole story. The A1C only gives us an average picture of your blood sugar, and that can be as misleading as a meter. Consider this: If your blood sugar ranged equally between 100 mg/dL and 200 mg/dL, your average would be smack dab in the middle at 150, right? That same 150 average can be created by a number set that runs from 50 to 250, which I’m sure we’d all agree is less than desirable.

While the A1C gives us a measure of the average, it gives us no clue as to the range of the blood sugar that created that average—and wide ranges in blood sugar have been implicated by recent research as playing a large role in the development of complications. That’s where smart testing comes into the picture. If you test your blood sugar strategically throughout the week, checking at different times (before and after different meals, and even in the middle of the night, occasionally) and combine that information with the A1C, you’ll be even smarter than the magic mirror. You’ll truly see all. Just using a meter, or just using the A1C, only gives you part of the picture. Used together, it’s…well, magical.

Of course, one of the best things the A1C tells us is trend over time. We can compare an A1C run today with one run three months ago, and with one run three months before that. We can see if our blood sugar control is stable, improving, or (((shudder))) getting worse. Done on a regular basis, the A1C test acts as an excellent canary in a coalmine: an early-warning system capable of telling you ahead of time if your diabetes is worsening.

Translating A1C Into a Language You Speak

Okay, you say. I see the value. But how do I understand the result? These numbers make no sense! Well, the Magic Kingdom isn’t going to help us out in this section, so we’ll have to go to Kansas to visit the wizard. If you are traveling 112 kilometers per hour down Interstate 70 in Kansas, will you get a speeding ticket?

I see your blank stares.

Despite what they told us in elementary school, the metric system never really took hold here in the States, did it? The answer is: no. If you’re zipping along at 112 kph, you are traveling at 69.594 mph, well below the 75-mile-per-hour speed limit.

Of course, you can still be busted for not wearing your seatbelt, or talking on your cellphone.

Did I get off track? Not at all, because A1C scores are like the metric system. They use a mathematical language we really aren’t fluent in. The score is a percentage of something we can barely grasp in the first place, so it can be hard to put it into a useful perspective in the trenches. We all know that our docs want our scores to be below 7.0. And we all know that at 9.0 blood has so much sugar in it, it’s literally toxic to the cells in our bodies—like having battery acid in our veins. At 14.0, most clinic-based testing machines max out, and while labs can clock much higher readings—up into the high 20s—that’s the level at which most doctors faint while reading the results.

What about a reading like a 7.3? Or 8.1? What do these kinds of not-in-target, but not-toxic-to-the-body numbers really mean? Well, just as you can convert metric to standard, you can convert A1C numbers into the traditional meter numbers of mg/dL—a language in which we are all fluent. The formula is:

28.7 x A1C – 46.7 = your A1C converted to a “meter number.”

If you hate formulas, there’s an online calculator here.

For instance, the A1C of 7.3 we were talking about means your average night-and-day blood sugar level over the last few months was 163 mg/dL. The 8.1 translates to 186 mg/dL.

Keeping Your Head In-Target, Rather Than Your Blood

What do you do if you fail the A1C test? First and foremost, don’t panic. The A1C isn’t intended to be a judgment of you. It’s simply a guidepost on the journey—a way of knowing if you are on the right road. A “bad” A1C doesn’t make you a bad person. It just means that you have some work to do.

I always say bad news is good information. Let’s say your A1C is toxic. It has come back at 13.8 percent. Your doc grimly fills your head with tales of blindness, amputation, and kidney dialysis in a misguided attempt to motivate you. Naturally, you are so depressed you just go home and eat Cheetos®. And strawberry ice cream. Because why not? You’re just going to die anyway, right? This actually happens to a lot of people.

I take a different view. I think a high A1C just shows that the therapy plan isn’t right for the patient. Maybe we need a different blood-sugar-lowering medication—or more of the one we’re using. Maybe we can look again at the person’s diet to see if there are any realistic improvements to be made. Oh, you’re drinking a six-pack of bottled green tea every day, because you thought it was healthy? Did you look at the Nutrition Facts label? That stuff has more sugar in it than regular soda!

If your A1C is waaaaaaaay too high, we know bad things will happen to you over time—but time is on your side, and there are many, many tools to help you lower your blood sugar. You need to improve the score (and lower it), but it doesn’t need to be done overnight. So…no test anxiety! The A1C is about guidance rather than judgment. Rather than fear it, you should look forward to it. And then you can say:

Mirror, mirror, on the wall, when will my A1C start to fall?

Wil Dubois is a diabetes treatment specialist with the Pecos Valley Medical Center in New Mexico, a rural non-profit clinic. He has type 1 diabetes, and is a health columnist and author who has published over two hundred seventy-five articles and four award-winning diabetes books.

Updated 11/16.


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