The hemoglobin A1c test, as we all know, is supposed to give a sense of your average blood glucose levels over the past three months. But here’s a question for you: have you ever tried to figure out what those average blood glucose levels actually are? Say you have an A1c of 6.5% — what, in mg/dl, does that translate to?
Try searching Google — it’s hard to find an answer. To quote from a post I wrote a few years ago (see entry from 4:45), that’s partially because:
“Not only is there no one standardized definition as to the correlation between A1c and mean glucose levels (JDRF says 1% = 24.4 mg/dl, ADA says 28.7), but different people have different correlations. For example, if you are a ‘high glycolator’ (more glucose sticks to your hemoglobin than the average) you can have a relatively high A1c but a low mean glucose. The speaker gave the example of a patient who had a 8.2% A1c, but a mean glucose of 159 mg/dl (he was speaking using the generally accepted idea that 7% roughly equals a mean of 154 mg/dl). Treat him more aggressively, and you’ll end up with hypos. And if you’re a ‘hypoglycolator,’ it’s the opposite.”
Well, just this week, a new paper was published in the American Diabetes Association’s Diabetes Care journal that provides a more solid answer to this question than I’ve seen — even though, as I must warn you, personal variability (as described above) means there’s still no precise answer. In the study, researchers wanted to find out what your average blood sugar would have to be in three situations — fasting, after meals and before bed — in order to achieve a particular A1c.
Here are their results:
A1c test results of 5.5-6.49% were associated with an average fasting blood glucose level of 122 mg/dl.
A1c test results of 6.5-6.99% were associated with an average fasting blood glucose level of 142 mg/dl.
A1c test results of 7-7.49% were associated with an average fasting blood glucose level of 152 mg/dl.
A1c test results of 7.5-7.99% were associated with an average fasting blood glucose level of 167 mg/dl
A1c test results of 8-8.49% were associated with an average fasting blood glucose level of 178 mg/dl.
The abstract only reveals two values for the post-meal and pre-bed glucose values:
An A1c test result of 6.5-6.99% was correlated with an average post-meal blood glucose of 139 mg/dl, and an A1c of 7.0-7.45% with an average post-meal reading of 152 mg/dl (unfortunately I can’t tell from the abstract how long after meals these numbers were taken).
An A1c test result of 6.5-6.99% was associated with an average pre-bed blood glucose of 153 mg/dl, and an A1c of 7.0-7.49% represented an average pre-bed value of 177 mg/dl.
More information on the study is here.
Hi it’s really great to know that you are here to support each other. I was diagnosed with Type 1 a few months back. This week I visited my Endocrinologist and she gave me a sample and prescription for Januvia (to lower my A1C, currently 7.4). The first thing I noticed from reading the associated material and visited the manufacture’s website, is that it should not be taken by patients with Type 1. Am I reading something wrong, or is my physician in error for proscribing this medication.
This is quite interesting. I recently tested at 5.5 a1C, and my fasting BS falls anywhere from 72 mg/dL-82mg/dL. I’m hard pressed to be over 120 mg/dL 1 hour postprandial. Most of the time I fall between 95-100 mg/dL – but I do control my portions, and I only eat about 100-125 carbs per day. Obviously, I’m nowhere near the associated FBS of 122 mg/dL. Personal variability indeed.
It seems to me that the bigger issue is that, historically, endocrinologists have not explained the A1c properly. It is my understanding that the A1c is more a reflection of the amount of glucose that sticks to red blood cells when your BG is over 150 mg/dl. Since red blood cells live 90 days (the typical timeframe for an a1c), your A1c will be more reflective of your more recent blood sugars, rather than the ones from days 10-20, for example, in that 90 day cycle. So, if you maintain a “dream” blood sugar of 126 mg/dl for 80 days,… Read more »
It is so frustrating. I think you have to hope you have a great Endo that truly understands both types of diabetes. I have been a T1 for 33+ years. I’ve seen the A1c change from 7% to… get this 5.6%!!! My last A1c was 6.8, which I was ecstatic about, but when I looked at my lab paper, it shows I’m “high”. And that I should be 5.6. Well, luckily my Dr. does not agree with that. Especially since I’m on a pump. He wants me in the low 7’s. But, it is very upsetting and discouraging to… Read more »