Retrospective #228: A1c and your estimated Average Glucose (eAG)

The glycated hemoglobin (Hb) A1c has become the new standard for assessing a patient’s diabetes status. It is a percentage, as for example the ≤7% default ADA target for a diagnosis of Type 2 diabetes. The percent is the amount of glucose attached to the surface of a hemoglobin molecule within a red blood cell.

Red blood cells typically live 2 to 3 months, so this is a surrogate way of determining the level of glucose in your blood 24/7 over that 2 to 3-month period. The ADA recommends that a Prediabetic’s A1c be tested at 2 times a year and, if you’re a diagnosed Type 2, 4 times a year. Medicare will pay for 4, unless more is deemed “medically necessary.”

Prior to using the A1c test, a clinician used two consecutive fasting plasma glucose tests that exceeded the ADA’s Standard of Care for Type 2 diabetes. Until 1997 that Standard was ≥140mg/dl. After 1997 it was lowered to ≥126. In addition, a new standard for Prediabetes was established: readings between 100 and 125mg/dl. If your lab tests are between 100 and 125mg/dl, and your doctor hasn’t told you that you’re Prediabetic, you might want to ask why?

The difference in units (% vs. mg/dl) has understandably led to some confusion and a disconnect. Besides, knowing your fasting blood glucose only tells a small part of the picture of your diabetes health. What happens to your blood glucose after you eat is what really defines how impaired your glucose tolerance is and the degree of insulin resistance you are developing. That is why the A1c test is a better indicator of your diabetes health than the fasting glucose test.

So, to resolve the disconnect and the confusion that has resulted, a copyrighted table has been developed at diabeteschart.org that creates a correlation between A1c % and estimated Average Glucose (eAG) in mg/dl.

From this chart, an A1c of 7% is equivalent to a whopping eAG of 154mg/dl. This is stunning. That means that, if you have an A1c of 7% (the AD’s recommended GOAL), your plasma blood glucose is higher than 154mg/dl for many hours each day, especially if your fasting blood glucose is in the 126mg/dl or lower range. Why is that important? Because, it is generally understood and accepted that ANY TIME YOUR BLOOD GLUCOSE IS ABOVE 140MG/DL, IT IS SLOWLY BUT INEXORABLY DOING DAMAGE TO YOUR MICRO AND MACRO VASCULAR SYSTEMS.

Because I have not been as vigilant as I should be in watching what I eat, my own A1c’s have been higher than I would like for the last year or so. Breakfast and lunch are easy for me, but at or after dinner, I have not always stuck to plan. As a result, my A1c’s are now almost always in the high 5s. An A1c of 5.8 is equivalent to an eAG of 120mg/dl, which means if my fasting blood sugars are in the low 100s, my postprandials are near or above 140mg/dl. That’s bad.

But my doctor, who adheres to the ADA Standard of Care, considers my blood sugar “in control.” How can I convince him otherwise? He is following the ADA’s Standard. So, I just have to establish my own Standard, and hope he goes along with my plan. So far, he’s “on board,” but in the future, if we see it differently, I’ll just have to change doctors.

I currently have a prescription to test twice a day. When I was learning about low-carb eating, my previous doctor (now deceased) wrote a script for 4 test strips a day. But now, I get by fine with 2. I always do a fasting test and use the second strip to test at other times, or just renew the prescription later.

Recently, while on an antibiotic to treat a tick-borne infection, I did a “continuous” (@ 2-hour intervals) test all day. I had these results:  9AM (fasting): 128; 11AM (2hr pp): 120; 1PM (4hr pp, before lunch): 125; 3PM (2hr pp): 120; 5PM (before dinner): 118; and 7PM (2hr pp): 179. Dinner was in a restaurant. I ordered 2 appetizers: 6 raw oysters, and then steak tartare with an egg yolk in the center. Then (here’s the bad), I helped my wife eat her large order of sweet potato fries that came with her “steak frites.” I should have ordered/eaten a side of roasted Brussels sprouts instead.

Result: all day long my blood sugars were higher than usual for me due to my body helping the antibiotic fight the infection, but they were stable. Then, after dinner, they “spiked” due to my indiscretion. I love sweet potato fries, but I paid a big price for going “off the reservation.” To see if it normalized, I should have tested 4 hours postprandial, but didn’t. I’m still on a single dose of Metformin (with the evening meal) to suppress postprandial gluconeogenesis.