A1Cs vs. Meter Readings


I got a letter published in Diabetes Forecast this month! Actually it was my mom who wrote in with my question because I was too lazy and didn’t believe it would get a response. Anyway, my question was: why do I persist with A1Cs of 7.4 if my BG Meter average is always about 135-140? This has gone on for years, over different meters. I tried CGMS for a few months, which showed spikes after meals so I started on Symlin. No improvement in A1C at all after 8 months of Symlin. I test about 6 times/day and am on the pump. I am properly trained in testing my blood sugar. I was wondering if my blood is weird somehow from being a quasi-vegetarian, or being Irish, or tall, or having low niacin or something nutritional like that. The letter is in the December 2007 issue on page 16. Any ideas?


Hey Grace!

Just statistically speaking, my first guess would be that perhaps there are times that you do not test when your blood sugar is higher than average… did you try writing out the times that you tested and make sure that you are covering the whole day? When you were on CGMS did you have highs at night or in the early morning?

I have about the same A1C (or a little higher) and my averages are usually 160-200… so it is puzzling! I hope that you are able to figure something out!


Jenny has a post on her blog about how fructose can raise your A1C, but not show up on your glucose testing. If you are eating a lot of fruits and vegetables this would be consistent with lower BG levels and higher A1C. You can find the post at http://diabetesupdate.blogspot.com/ The date was October 17 so if you go into the archives you can read it. It’s very interesting. I have also been surprised at the discrepancy between my meter and my A1C results and I am pretty sure that is the reason. Another thought I have is that if you are testing at 2 hours after meals you might be up in the higher range for the several hours a day that you are not catching on the meter. If you are testing at 2 hours you might want to look at one hour just to find out if that is the case. How high did you go when you were on the CGMS? When I was first diagnosed I had an A1C of 7.3. No-one could understand it because two hours after every meal I was under 120. I was mostly vegetarian also, eating a lot of rice, beans, vegetables and fruit. what I finally figured out was that I was going up to 180-200 after every bite of food and even though I did eventually go down, I tended to “graze”, eating every couple of hours, so I swung right back up. Even so, it was hard to figure why my A1C was so high since my fasting BG was in the 80-90 range. I am also Irish and tall so maybe that is the true reason :-> On a low carb, mostly raw food diet, my A1C is now 5.6 and the highest readings I see are about 120 at an hour, going back to under 100 at two hours. Since this seems to be almost completely normal I am curious to find out what my next A1c results will be like in January. If they are still in the mid 5s I am guessing that fructose is the culprit but since my numbers are close to normal I am not planning on cutting out fruit.


IMO, it’s the area under the curve that’s important. if you plot (or just consider) bg versus time, and look at how long you spend at a given bg level, that will more likely reflect your A1c. PS, I was good at getting an A1c below 7, without good control, by being hypo. a lot. the wild swings kept my a1c down, but I still had high peaks in bs after meals.


Kristin - Thanks for the reply! The CGMS showed me flat as a pancake at night and in the morning. My overnight basals are good. - Grace


When in doubt, integrate. Makes perfect sense.


http://care.diabetesjournals.org/cgi/content/full/25/2/353 After reading your entry, Jenny’s blog and this abstract, I have some serious thinking to do about my diet. I have never considered eating less fruit. I’m also a “grazer” but I only thought that was a problem if my bolus or basal rates were off. I test both before and after meals, but maybe I’ll test 90 mins after meals instead of 120 mins. Also I had quit using Symlin since I got no results but maybe I’ll restart that. When I used the CGMS it showed me going to 200 or so after every meal, but no other major spikes on a regular basis. The spike would always come back down within 3 hours or so. I bet the liver is involved in this somehow. I should probably change my diet to avoid those spikes, but I don’t want to eat an Elvis diet…


A1c assumes red blood cells live for 120 days. If yours live longer than that, your A1c would be higher than expected. If you’re anemic or if you donate blood, your A1c would be lower than expected. People who lack a spleen have red blood cells that live longer than 120 days, and I’m sure there’s also genetic variation in the lifetime of the rbc’s.

Certain unusual hemoglobin variants, such as that found with thalassemia, can also affect the A1c because those hemoglobins behave differently in the tests.

I’m sure there are other factors that affect A1c that people haven’t figured out yet.


Gretchen, I don’t think how long your red blood cells live makes any difference to your A1C reading, only to how often you should have one taken. It’s just a average.

The hemoglobin in the red blood cells can bind with blood glucose. The higher your blood glucose when the blood cell is created, the more glucose is bound up in the hemoglobin. The normal assumption is that the reaction is not reversible, so once the glucose is bound, there it stays until the cell dies. The A1C measures the total glucose bound up in all of the blood cells tested, which gives an average of the sugar levels over the life of the bloodcells. If your bloodcells live longer or shorter that the normal average life (3 months), then your A1C measures an average over a longer or shorter period.

There are some people who now believe the reaction IS partially reversible (the amount of glucose bound in the hemoglobin can change if the blood sugar level changes) and so the A1C is heavily weighted towards the blood sugar levels of only the last 3 or 4 weeks.


Yes it does make a difference. Once glucose gets attached to hemoglobin, it mostly doesn’t come off. But your body constantly destroys old red cells and makes new ones. The new ones don’t have any glucose on them. The longer RBCs remain in your bloodstream, the more likely they’ll get glucose attached. If you suddenly drained out all your blood and replaced it with freshly made blood, your A1c would be close to zero.

Obviously, unless we encounter a vampire, we’re not going to drain out all our blood. But donating blood or having internal bleeding will lower the concentration of glycated hemoglobin, which will be replaced by unglycated hemoglobin, so the percentage glycated will go down.

Do some searches on “A1c anemia” or “A1c spleen” and you’ll find more information on this.

The very first step in this process is reversible (which is why I said mostly), but not the later steps.


Here’s a good link.

You have to register to read, but it’s free. A quote from the article:

“The reason for these differences between “high” and “low” glycators was originally thought to the result of interindividual differences in tissue glycation, but recent data suggest that much of these differencies can be explained by the fact that high glycators seem to have red blood cells that survive for longer than low glycators.21 Even if there is to be a change in the HbA1c set point, then it seems likely to be related to changes in red blood cell life rather than glycaemia or glycation rates.22”


Thanks for correcting me, Gretchen. I thought the glucose binding occurred when the blood cell was formed. Your posting makes perfect sense to me now that I know better. Do you know how much variation in blood cell life affects A1C?


Look at the article I posted the URL for. I think they said people with the same glucose control could have A1cs as much as 2% different.


I wouldn’t think two readings that high would have much effect. But I’m not a mathematician, so I can’t calculate how much. I think the alt.support.diabetes home page used to have a discussion of calculating the A1c and how to weight it.


Have you had your a1c tested at any other labs? Even if you’re having blood drawn at the same doc, maybe they changed equipment, assays or are sending the blood off to a different lab?

When I moved to Germany my control didn’t change from what it had been in the US and my a1c’s kept coming back at 7.0 to 7.4. I was so upset I’d leave appointments crying. It was impossible to have a meter average of 128 and an a1c of 7.2, dammit! And I check up to 10 times a day! Well, I suspected maybe the meter they gave me (since I couldn’t continue to use my one form America… it’s not sold here) was wrong. My endo actually had me do all day lab versus meter tests from the same finger stick to prove my meter was indeed accurate. (It was, too. Wow. Really close to the lab every time! It’s an Ascensia Contour, btw.) Well, he also checked my a1c, since it was usually tested at a more convenient lab for me… that of my primary care doc’s. Guess what? My primary care’s lab had said 7.2 and my endo’s lab said 6.5!!! And this was no more than 2 weeks apart! So I wasn’t crazy, it was just that my primary care’s lab was giving back much higher numbers! And even my endo’s lab’s a1c test is calibrated to a higher level than the labs I used in America. Which means, my old lab in America would say my a1c is 6.2. My endo in Germany would say 6.5. My primary care in Germany would say 7.2! Not all labs are the same and this can be at least one reason the finger sticks or CGM don’t match up with the a1c.