Diabetes Simplified: A1C Testing
The Science (or Black Magic) Behind A1C
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 glycated hemoglobin test. There're all the same thing. This is a lab test that allows your doctor, by consulting with the 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 on 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%... 7.8%...8.3%...9.6%...12.4%... and so on. Most A1C scores are only given in 10ths of a percent, but some labs report 20ths as well so you might see an A1C of 6.79% or 8.32%.
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, how much powdered sugar has stuck on the doughnut hole.
The keys to the test's success are the fact that you can't scrape the sugar back 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; and the fact that a typical red blood cell only lives for 90 days. Any A1C test won't show what the sugar was like beyond 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 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. So, 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 and 200, your average would be smack dab in the middle at 150, right? But 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.
So while 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 has having a large role to play in developing complications. That's where smart testing comes into play. If you test your blood sugar strategically throughout the week, checking at different times, such as 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.
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