Continuing the discussion from Tips to quickly lower blood sugar readings:
As often happens in our discussion threads the discussion focus veered off topic. So when @Eric30 suggested that we start a separate thread, I decided to do just that.
I’ve always checked my fingerstick blood sugar more than the average person. For many years I averaged between 10-15 checks per day. Eight years ago I started using a CGM and my quantity of blood glucose data skyrocketed.
With the volume of data I collected I had confidence that it revealed representative blood glucose averages for 14, 30, 60 and 90 day periods. I was also aware that a math formula could be used to convert an average blood glucose number to its corresponding A1c number.
What I found when I did this over the years is that my lab derived A1c corresponded to a significantly higher average blood glucose than reported by my fingerstick meter and CGM. Stated another way, my meter and CGM averages predicted an A1c 0.5-1% lower than the lab measured.
I’ve read that the A1c test is based on an assumption that red blood cells live for a certain duration, something within 90-120 days. I’ve also read comments from the medical literature that for people whose red blood cells live longer or shorter than the assumed longevity in the formula, then their A1c would read falsely higher or lower. In my situation, with a lab A1c 0.5-1% higher than the averages my meter and CGM predicted, it made sense to me that my red blood cells may live longer than the number built into the A1c protocol.
I’ve raised this issue in a few other threads and was surprised that most responses say their meter and CGM averages do a very good job predicting their A1c’s.
I know there are other explanations for my experience. The obvious one is the fact that I’m basing my conclusion on averages from my blood glucose meter. Our meters are not the most accurate tools but it’s what we have.
At my last A1c blood draw, I did three fingersticks and recorded these numbers: 80, 85, 86 mg/dL (4.4, 4.7, 4.8 mmol/L). This calculates to an average of 83.7 (4.6). The lab came back with a glucose value of 82 (4.6), a difference of only 2%. So I conclude that my meter (Accu-Chek Aviva Connect) is reasonably accurate and using it to calibrate my CGM keeps my CGM numbers relatively accurate. I like to do this exercise at every A1c lab draw.
When my blood was drawn for the glucose and A1c, here are the averages from my CGM along with the predicted A1c:
90-day average = 99 = 5.1%
60-day average = 94 = 4.9%
30-day average = 90 = 4.8%
14-day average = 87 = 4.7%
My doctors have told me over the years and I have read that the most recent period is weighted more than the earlier periods. So, the last two weeks are weighted more heavily than the first two weeks of the three-month period. I think my CGM averages predicted an A1c of 4.9%. My A1c came in at 5.5%.
Now, I’m not complaining. I’m thrilled that my A1c is in the “non-diabetic” range. So I just used a lot of words to express a simple thought: I believe the explanation for my higher than expected A1c is due to my red blood cells living longer than the average.
@Eric30 was interested in the explanation of why I think my red blood cells live longer than the A1c formula presumes. I’d be happy to hear your thoughts, if any. Sorry, @Eric30 if the explanation provides too much detail.