Over the last few years doctors are increasingly relying on a test called hemoglobin A1c to screen for insulin resistance and diabetes. It’s more practical (and significantly cheaper) than post-meal glucose testing, and it’s less likely to be skewed by day-to-day changes than fasting blood glucose.
What is hemoglobin A1c?
Sugar has a tendency to stick to stuff. Anyone that has cooked with sugar can tell you that. In our bodies, sugar also sticks – especially to proteins.
The number reported in the A1c test result (i.e. 5.2) indicates the percentage of hemoglobin that has become glycated (stuck to sugar).
Why is hemoglobin A1c unreliable?
While this sounds good in theory, the reality is not so black and white. The main problem is that there is actually a wide variation in how long red blood cells survive in different people. This study, for example, shows that red blood cells live longer than average at normal blood sugars. Researchers found that the lifetime of hemoglobin cells of diabetics turned over in as few as 81 days, while they lived as long as 146 days in non-diabetics.
This proves that the assumption that everyone’s red blood cells live for three months is false, and that hemoglobin A1c can’t be relied upon as a blood sugar marker. In a person with normal blood sugar, hemoglobin will be around for a lot longer, which means it will accumulate more sugar. This will drive up the A1c test result – but it doesn’t mean that person had too much sugar in their blood. It just means their hemoglobin lived longer and thus accumulated more sugar. The result is that people with normal blood sugar often test with unexpectedly high A1c levels.
This confused me early in my practice. I was testing blood sugar in three different ways for all new patients: fasting blood glucose, post-meal blood sugar (with a glucometer) and A1c. And I was surprised to see people with completely normal fasting and post-meal blood sugars, and A1c levels of >5.4%.
In fact this is not abnormal, when we understand that people with normal blood sugar often have longer-lived red blood cells – which gives those cells time to accumulate more sugar.
On the other hand, if someone is diabetic, their red blood cells live shorter lives than non-diabetics. This means diabetics and those with high blood sugar will test with falsely low A1c levels. And we already know that fasting blood glucose is the least sensitive marker for predicting future diabetes and heart disease. This is a serious problem, because fasting blood glucose and hemoglobin A1c are almost always the only tests doctors run to screen for diabetes and blood sugar issues.
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What blood sugar markers are reliable?
Testing accurately for blood sugar is like putting pieces of a puzzle together. Fasting blood glucose, A1c and post-meal blood sugar are all pieces of the puzzle. But post-meal blood glucose testing is by far the most reliable and accurate way to determine what’s happening with blood sugar, and the most sensitive way of predicting future diabetic complications and heart disease.
For more on why post-meal blood sugar is a superior marker, read my article When Your Normal Blood Sugar Isn’t Normal (Part 2). To learn how to test your post-meal blood sugars at home, and what healthy targets should be, read my article How to Prevent Diabetes and Heart Disease for $16.
Another useful – but underused – blood sugar marker is fructosamine. Fructosamine is a compound that results from a reaction between fructose and ammonia or an amine. Like A1c, it’s a measure of average blood sugar concentrations. But instead of measuring the previous 12 weeks like A1c, fructosamine measures the previous 2-3 weeks. And unlike A1c, fructosamine is not affected by the varying length of red blood cell lifespans in different individuals. Fructosamine is especially useful in people who are anemic, or during pregnancy, when hormonal changes cause greater short-term fluctuations in blood glucose levels.
To put the most accurate picture together, I like to have all four: fasting blood glucose, A1c, post-meal glucose and fructosamine. But if I only had to choose one, it would definitely be post-meal glucose.
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Can I pass the a1c test and still have diabetes? For 9 daysy feet and calves are cramping, I have pain in both feet, hands and legs, thirsty always, urinate constantly and I’ve list 25 ps in 6 months?????
It looks like an A1c of 7 is “passing” at most labs. Not sure what you are calling a passing level.
That high a level is an invitation to complications.
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Hi Chris,
I am a 41 year old female with a BMI of 18, no family history of diabetes, who leads a very active lifestyle, running about 20-25 miles per week. I have never been overweight. I recently had my HgA1c measured at 5.9, so I decided to start checking my blood glucose at home. All of my fasting measures are in the 80s. My accuchecks 2 hours after breakfast have been 80s-90s consistently. I have noticed that, depending on what I eat, my glucose 2 hours after lunch ranges from 100s to as high as 137. The numbers in the 130s seem to occur after I eat over 80 gm of carbs. When I keep the carbs to less than 50 gm per meal, I tend to stay below 120 2 hours after eating. I generally do not snack in between meals. What is your take on these numbers?
Also, in my research, I ran across this article about a study of HgA1c performed on cyclists whereby HgA1c increased with increasing intensity of training. What are your thoughts on this? Do you think there may be some physiological adaptation with endurance training that causes HgA1c to be inaccurate in this population?
Thanks for all of your helpful information!!
Chris, I appreciate the articles. I am new to this, but my situation is a little different from others I’ve read/talked to. My A1C came back 8.3 – but my triglycerides are low in the normal range. Glucose at the time was at 177, but I was also tested in the late afternoon. I had been on warfarin for 7 months, but was taken off 2 weeks before my blood work was drawn. Have you heard of this before. I have been told by cardiologist, GP and other people and doctors that the correlation between A1C and Tri’s are both usually high.
Good article. Doctor #1 said I was diabetic. Went to an endocrinologist #1 and he agreed. Put me on Metformin and later Glimepiride. Even had me take a 72 hour continuous glucose monitoring and showed high levels of glucose, but A1C usually ran deceptively low. Sticks and A1C did not correlate. No one could give me a reason why. Since A1C was normal, Dr. #1 said I don’t need meds anymore. I knew that was wrong because if I stopped the meds, glucose woule go back up. Dr. #2 said yes I do need meds. I didn’t go to medical school, but when my tests didn’t correlate, I knew at least one of the test had to be wrong, but neither doctor could explain why. Went to six hours of diabetes education classes at the hospital and the certified diabetes educators didn’t know why I was abnormal.
Went to a second endocrinologist, doctor #3, and he immediately said I had a hemoglobinopathy. He kept me on the previous meds plus added Farxiga. Farxiga allows kidneys to pass sugar out through the urine instead of recycling the sugar. Now my fasting sticks have dropped by half to 120-135.
I have to get fructosamine tests in the future to get a more accurate reading. A1C tests may be okay, but doctors need to realize its not the only test out there and certainly not 100% reliable for 100% of all patients. If different tests don’t match, ask questions until someone can answer them. Patients have to be in control of their own health care and not turn everything over to others. Doctors and the Internet are resources that can give patients information to manage their health.
Checked a couple of diabetic websites and they didn’t even have the term hemoglobinopathy in their search engine. That’s scary and shows that there is a problem with diabetes education. Called one of the sites and never could get through. Got annoyed for ten minutes of being on hold while their messaging tape kept asking for donations.
Glad you have this site and continue to pass the word.
Hi Chris,
I had my A1C a year ago and it was 4.9 which is a low but normal range. I have hypoglycemia. Should I get tested once or twice a year? Since I’m not diabetic, my bs levels are mostly at a low. By low I mean, there’s times I wake up with it at 62-75. Don’t feel good at those numbers. I do eat 5-6 small meals a day to keep my bs levels up. It can get erratic. It could drop to 73 after only 2 hours after eating! Don’t do any sugar whatsoever. When it’s in the 60’s or even 70’s, I’ll drink a little milk to bring it up. Was tested for insulinoma..do not have that. It’s just a constant battle to keep my bs levels at a normal range. My doctor said I’m doing everything right regarding my diet since food is my medicine, so there’s not much the doctors can do. I feel the best when my bs levels are in the 80’s and 90’s which will be at that range after I eat. I usually don’t eat anything after 6:00pm, so by the time I wake in the early am and I mean early, sometimes I think my bs levels wake me up, as I said, my levels could be in the 60’s or 70’s. Anyway..I’d appreciate any feedback you can give me. Also..I don’t overdo carbos, don’t eat white potatoes, white bread, any junk food. I eat protein at every meal, salad, veggies, cottage cheese, cheese, lowfat (2%) yogurt, milk, chicken, turkey, olive oil, flax seed, beans. As you can see, my diet is pretty good, but yet..my blood sugar can be so crazy!!! Thanks again for listening and any input that you feel could help me…
Hi Chris,
I had my A1C a year ago and it was 4.9 which is a low but normal range. I have hypoglycemia. Should I get tested once or twice a year? Since I’m not diabetic, my bs levels are mostly at a low. By low I mean, there’s times I wake up with it at 62-75. Don’t feel good at those numbers. I do eat 5-6 small meals a day to keep my bs levels up. It can get erratic. It could drop to 73 after only 2 hours after eating! Don’t do any sugar whatsoever. When it’s in the 60’s or even 70’s, I’ll drink a little milk to bring it up. Was tested for insulinoma..do not have that. It’s just a constant battle to keep my bs levels at a normal range. My doctor said I’m doing everything right regarding my diet since food is my medicine, so there’s not much the doctors can do. I feel the best when my bs levels are in the 80’s and 90’s which will be at that range after I eat. I usually don’t eat anything after 6:00pm, so by the time I wake in the early am and I mean early, sometimes I think my bs levels wake me up, as I said, my levels could be in the 60’s or 70’s. Anyway..I’d appreciate any feedback you can give me. Also..I don’t overdo carbos, don’t eat white potatoes, white bread, any junk food. I eat protein at every meal, salad, veggies, cottage cheese, cheese, lowfat (2%) yogurt, milk, chicken, turkey, olive oil, flax seed, beans. As you can see, my diet is pretty good, but yet..my blood sugar can be so crazy!!! Thanks again for listening and any input that you feel could help me…also I wanted to add..I take 50mcg. of Synthyroid daily for my low thyroid, I’m 118-120 lbs which is perfect for my 5’5″ height and my BMI is 19
Cinzia, I was surprised I finally found correspondence from another hypoglycemic person. I have suffered from it as far back as I can remember, maybe 8 years old. My sister and I would both call it “that far-away feeling”, since that’s how we would feel. It wasn’t until my sister became a nurse and suffered an episode. She had her blood sugar tested and it was 50! She then told me it was hypoglycemia. I am now 58 and was recently in a motorcycle accident. The nurse came in and asked me how I felt. I said fine, except for the road rash. She said “Really? Your blood glucose is 60.” I told her yes I have hypoglycemia and I don’t usually feel it until it gets very low. I have found that eating five or six small meals a day helps more than anything. Drinking coffee early in the morning can cause an attack. Not eating breakfast can cause an attack. I usually get it if I don’t eat much for breakfast, drink coffee and take a brisk walk. When I stop walking, it comes on… Since I’ve had it 50 years, I guess there’s not much to worry about.
AIC. Anyhow have (other than me) a LOW retic count? Any doctor check that? I have a very very low retic count and wonder how that affects my a1c reliability. Thank you.
While diabetics do have shorter lived red blood cells, and that does matter, when comparing diabetic A1Cs, you are being compared to other diabetics generally, not the normal non diabetic population. So this does give you a good idea of how you stack up to other diabetics, as well as monitoring your own progress by comparing your own readings over time. So in other words, the targets for good control are diabetic ones which take this into account as do the studies that produce these targets.
So there are indeed two different references here, longer and shorter lived, diabetic A1C targets are higher but that’s pretty much by design.
i was recently tested for Hemoglobin A1c because i presented to an endocrinologist with extremely low blood glucose on lab test and some scary symptoms, not the ordinary hypoglycemia symptoms. My A1c was 4.7 which registered as low (L) on the lab print out–it was only slightly low. Does a low score on this suggest a possibility of short-lived RBCs? Does it have any relationship with extremely low blood glucose? my result at the lab, fasting, was 32mg/dL.
Not long after that i got a home glucometer and i get the same kind of results on that as the lab got, in the 20s and 30s first thing in the morning, every day.
did not know i had hypoglycemia until i had that lab test, though i had had one episode where i woke up with ataxia, i fell while walking to the bathroom first thing in the morning, i got up and immediately fell again. I soon found that i had very impaired coordination. i did not know why and i was very worried. Eventually i wanted to have breakfast but had great difficulty holding the measuring cup under the faucet, to get some water to heat, to make instant oatmeal, i lacked the coordination to get the water into the cup. I persisted and did make the instant oatmeal (pour hot water onto flakes and it’s done), and i got my lap top and was eating the oatmeal and i suddenly was aware that the symptoms were going away. Previously i had been unable to type. While eating the small amount of oatmeal, i realized i could type. That was about a month before the lab test.
Since it only happened that once, i put it out of my mind. About 5 days after the lab test, i had the second episode, worse than the first, i woke falling out of bed to the floor, couldn’t use my arm to break the fall, i didn’t have the coordination. i sat on the floor, i could not get up and walk, I crawled to the kitchen and began eating a piece of whole grain rye bread, sitting on the floor, and before i had finished one bite, i felt the symptoms go away and i knew i could get up and walk.
So since that day, i have thought of myself as ‘hypoglycemic.’ I look pale, i feel groggy, i am in poor shape. I have had some blood tests, a non fasting repeat of blood glucose was 63 (after eating three meals in the previous 4 hours), i had the A1c scoring 4.7. More recently i’ve had another lab test which included non fasting glucose and insulin. Glucose was 53 (i had eaten about an hour before the test, whole grain rye bread, tuna, apple), insulin was 58, which is high.
I was wondering about the A1c and after reading this article, am wondering if this could be evidence that my RBCs are short-lived. I have no results showing anemia, most recent result in late Februarly, was 4.60 and previous tests didn’t show low RBCs. Other CBC results were normal.
After realizing i was hypoglycemic, i started eating frequent meals and i started feeling better and my head got clearer, but then after a couple of months, i was slacking off on the number of meals and i was going back to my previous habit of not eating breakfast when first arising but going for a 1/2 hour walk, doing some yoga, maybe straightening up the house. I began feeling less well and my glucose results on my home meter were getting lower and lower.
Two weeks ago, i woke up one morning laying on my back on the floor by the foot of my bed, having no idea how i got there. i couldn’t move, i couldn’t get up, until about 10 minutes went by and then i could sit up. i saw that i had knocked over my valuable guitar which was laying on its face on the floor, i have no memory of that.
i crawled to the kitchen and ate a piece of rye bread, and was able to get up and walk, but not feeling too good. The next morning it was similar. I woke laying on the floor next to my bed, no idea how i got there, unable to get up, stuck on my back, struggling to get up, no results, for about 10 or 15 minutes, it was like being in a dream state, i did not understand what was going on, i had some weird thinking, like a dream, and then gradually i got to a normal state of consciousness and ate a protein bar which i had put in my room the night before just in case, and then i could walk to the kitchen and make breakfast.
Since then, i’ve been eating very frequently and was also eating during the night and before getting out of bed in the morning.
I have been using a home glucometer since early March, i always have really low glucose in the morning. Once in a while i get a result int he 40s and cheer because that is such a good result for me–the 40s is high for me in the morning, i hit about once every 2 or 3 weeks. When i started eating a lot, including during the night, the results on the meter began increasing, the 7 day average was in the 60s. But then, i stopped eating during the night, it seems very unhealthy to me, i hate doing it and can’t sleep, and i don’t know if that is why but my numbers have been going down.
The doctor who saw me on Monday and referred me to another endocrinologist described me as pale and fatigued (he was recording his comments, like chart notes). I saw my Chinese doctor yesterday and she looked very worried about me, she said i was pale and she emailed me this morning and asked how i was and told me she wanted me to come in for a treatment.
The GI doctor that the first endocrinologist sent me to said he thought it was odd that no one had taken insulin levels and said that insulinoma should be ruled out based on the history. So, he ordered blood tests that included glucose and insulin, he referred me to the second endocrinologist who i will see in 5 days, the earliest appointment i could get, despite reporting my symptoms. I want to know what testing i should ask for to help diagnose what is going on.
I meant to check that I wish to have any follow up comments sent to me. I am early 50s and exhausted all the time. Thank you so much.
Hello. You have been so helpful. My issue is that I have a very very low Retic count. But I do not have Anemia. I have searched for days to see if my Retic count could be giving me a falsely low A1C (which is 5.6) as my post prandials and fruct are very high and I am trying to make sense of it. Thanks!
My question is I had an A1C check because I went to ER with low blood sugar but mine came back at 5.6. I was told I have reactive Hypoglycemia. I am on a strict diet of no more than 7g of sugar per meal and no more than 27g of carbs per day. I am totally confused on why my blood sugars will spike into the 300s but even after eating what I am supposed, an hour later, mine will drop to the lower 50s and I feel like crap. Also, the one hour checks after meals don’t work for me, and the doctor couldn’t explain what was happening because it went against “text book”. My sugars always spike about 5 to 10 minutes after i eat but drop to low levels after that hour mark, so it’s not an accurate reading. I failed my glucose test and can not take that anymore either…but how can i fail it, and told it’s hypoglycemia? Confused person over here…..
Can anyone tell me if MDS diagnosis can increase blood glucose levels?
For those wanting to take readings before and after meals, get a home blood glucose meter and test strips. The cost will be less than a doctor’s visit and take a lot less time.
Walmart Relion Ultima has some of the lowest priced testing meters and strips and the strips are individually foil wrapped so not exposed to air every time you test.
You can only use the type and brand of test strips that are specific to your meter.
When I went to Diabetes School ordered by my doctor 12 years ago they said the Reli On by Wal-Mart was the worst most unreliable meter to get !!! I now have the One Touch Verio meter with gold test strips that cost my insurance over $150.00
for 100 but my glucose readings match the labs & my AIC !!! You
get what you pay for, One Touch Ultra is good also but reads 10 mg/dl lower than Verio !!!
I have a hemoglobin count at 18 and a ‘crit of 54.1. Will this affect my A1c? Thanks
Anyone know anything about the concept of high glycators vs. low glycators? This is another variable in determining HbA1c levels that I think I read about somewhere.
My wife tested at 5.7% A1c which represents the lower bound for increased risk for diabetes. Given that her resting heart beat is much lower than the average population (50 or less BPM), would that increase the lifespan of RBC, and therefore increase the result of the test? She also had 12 radiation therapy sessions on one cervical vertebra for bone metastasis, and I was wondering if that also may change RBC turnover therefore affecting the result of the test.
I am glad I found this article. I used to worry about my A1C all the time and believe the worry raised my blood sugars. After the latest article where the person say’s they can relax now and not be stressed was nice to read. I am 72 now and have regularly run high A1C’s mostly in the 8’s and also in the 9’s since I have been checked by this test yet I have no trouble with any diabetic problems. My eyes are fine and all my organs. So I never have been convinced the test is the God’s truth! I have been on insulin since 1995. I told my Doctor about this article but he dismissed it and said “You can’t believe everything you read on the computer”. Well as a living example of the way I respond to A1C tests I think I am! I am sure my blood cells are the rebellious type to this test by now. I am not worried at all about it anylonger!
Thanks for helpful article, Chris.
I’d like to add, however, that A1c results can be skewed both upwards and down by in response to differing kinds of anemia. With iron-deficiency anemia, for example, my understanding is that A1c results can be skewed misleadingly high.
The A1c test is complex and controversial, as you have pointed out.
Hi Chris,
This is such an informative article. I would like to know the best time to check my post-meal glucose.
Thank you.
Forgot to list my fasting sugars for the past three days: 129, 141, 133.