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HbA1c test results don't tell the full story

November 12, 2015 by Scott Johnson

It’s often viewed as the number to rule all numbers. But hemoglobin A1c (HbA1c) test results can be misleading and don’t tell the full story. As I learned in my teens, the HbA1c test shines a light on things I was trying to hide.

Overall, It’s not good at getting to the details of blood sugars, but when used with other pieces of information it can draw attention to (sometimes unseen) problem areas in our diabetes management, and that’s a good thing.

How do HbA1c test results work?

Let’s take a quick look at the basics of the HbA1c test. A certain amount of sugar in your blood sticks to your red blood cells and can’t be unstuck. It’s there for the life of the cell, which is, on average, about 8-12 weeks.

Those red blood cells in your body are constantly recycled, and by checking your HbA1c value every 8-12 weeks (or as often as recommended by your doctor – the ADA recommends at least twice a year), you get to see a fresh new grouping of them.

So – A higher blood sugar for a longer time means more sugar on more cells – which means a higher HbA1c. Get it?

Ideal HbA1c range

HbA1c goals are very individual, which makes sense. We’re all different, right? Of course, there are reference values as a guide, and that’s a good place to start.

The ADA suggests an HbA1c of 7%, but also say that “more or less stringent glycemic goals may be appropriate for each individual.”

Why have different goals? Because, as you know, there’s a lot to consider with diabetes. Avoiding lows (hypoglycemia) while pushing for lower A1c’s is really important because low blood sugars are immediately dangerous. It’s simply not safe to push for a very low HbA1c if you’re having a lot of lows, so your doctor might adjust your target up a little bit.

Additionally, your doctor should know if you have any conditions that may affect your HbA1c, such as sickle cell anemia, heavy bleeding, very low iron levels, kidney failure or liver disease.

Ideally, you’ll work together with your doctor to find a comfortable HbA1c goal that keeps you safe and healthy.

HbA1c’s dirty secret

The HbA1c is an average.

Dust off those old math lessons and think about how averages work. You can have two very different stories – one with pretty stable blood sugars, one with wild fluctuations – that equal the same HbA1c.

Dr. Stephen Ponder, a pediatric endocrinologist who’s been taming his diabetes monster for about 50 years, explains it very well in this graphic we’ve adapted (with permission) from his book, Sugar Surfing.

Graph adapted by mySugr from Sugar Surfing showing different groupings with same A1c

It’s a great reminder that HbA1c’s are not very good at details, and you still need to take a closer look.

Take the time to dive into your numbers and make sure your HbA1c is coming from details you want. Standard deviation is one way to do that. Standard deviation shows how much your BG’s are fluctuating.

According to another favorite, Think Like a Pancreas by Gary Scheiner, a good standard deviation is less than one-third of your average. Ideally, you want an in-target average with a low average standard deviation.

How to Estimate your HbA1c

You don’t even have to crunch any numbers. We do it all for you (along with average and average standard deviation) in mySugr.

Sketch showing mySugr Logbook's estimated HbA1c feature

From now on, the top right of your graph will display your estimated HbA1c – assuming you’ve logged enough blood glucose values. How many values do you need?

An approximate average of 3 BG’s per day over seven days

Sketch showing a calendar with the data requirements for mySugr Logbook's estimated HbA1c feature

Without enough data, the estimated HbA1c level is not displayed, as you can see here. The progress bars around the circle fill as you log more BG’s. Keep feeding mySugr data, and you’ll have your estimated HbA1c in no time.

But please, keep in mind that this is an estimate and may differ from the laboratory value. Enter more values and mySugr can do a better job estimating.

mySugr Logbook screenshot with estimated HbA1c

Keeping an eye on your HbA1c can make a big difference, as even small improvements have shown great reductions in the likelihood of complications. With the estimated HbA1c feature we hope we’ve made it easier to know where you are so you can get where you’d like to be.

And can we toast to no more nasty surprises when your doctor delivers your next HbA1c result? Cheers!

Pro Tip: Keeping your overnight blood sugar in the green is a quick and easy way to improve your HbA1c. Why? Think about it. It’s a large portion of the 24-hour period where you don’t have to do much, or deal with many variables. Sure, there will be some work up-front to troubleshoot problems, but once you get your overnight BG’s stable and on target, you fix one-third of your HbA1c. Easier said than done (like most things in diabetes), but totally worth the effort.

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