Hemoglobin is the protein molecule inside your Red Blood Cells (RBCs) which transports oxygen from where it enters the simple squamous epithelial tissue that forms the alveoli in your lungs which makes them function to the tissues in the rest of your body that need access to that oxygen but are too far away for passive diffusion. That is to say, your red blood cells have this special ingredient which holds onto oxygen that passively diffuses into them from your lungs and holds on until the conditions are right for it to dump that oxygen and picks up some of the CO2 (most becomes bicarbonate and just rides in the plasma but I digress) for return to the lungs to exhale the waste product.
What am I going on about hemoglobin for? Well, that protein makes up 97% of RBC’s dry weight. Hemoglobin A is the primary constituent in adults, and through a process called chromatographic fractioning you can use ionic charge to separate different groups of hemoglobin A from hemolyzed erythrocytes (RBCs broken open to release the hemoglobin). There are 5 minor components you find as a result of this chromatography, HBA1a-HBA1e (1 a - e). In 1968 Dr. Samuel Rahbar MD, PhD was evaluating blood samples for the detection of hemoglobinopathies when he made the discovery that HBA1c (Commonly shortened to A1c) was elevated in the diabetic patients whose blood he tested. That variant of hemoglobin was confirmed to be hemoglobin with a hexose (in this case glucose) attached, but later research with radioactive iron would confirm that the fraction of HBA1c increased 2.8x faster in diabetic mice than controls. This is non-enzymatic glycation, exposure to high blood glucose levels causes chance interactions that leave hemoglobin glycated, hence the measure being a powerful measure for average blood glucose levels in diabetic patients over the 3-month average lifespan of RBCs.
A1c now dominates Diabetes from diagnosis to management to bragging rights on the internet, and that last one is where I arrive on this scene. In September of 2025 I was diagnosed with Type 2 Diabetes Mellitus, a family heirloom. I managed accelerating the diagnosis to an early 30 years old in part because I was employed as a Software Engineer (a perfectly sedentary life if you so choose) and in another part because I am a diagnosed high functioning autist with a lot of comfort foods (sour patch kids) that I was eating with reckless abandon. But after finally managing to get diagnosed with an A1c of 12.2% (very high, normal is 4.5-5.6%) I found myself on Reddit, a place I generally dislike, enjoying the company of my fellow diabetics and the starkly contrasting supportive nature of the t2 subreddits.
There’s a concerning problem though: I don’t know if my peers know what A1c actually is, or I suspect some of them would brag less and others would worry less. These groups are the frail or anemic and athletes, respectively. These populations will see artificially deflated or inflated A1c levels because of the factors that confound (interfere with) this lab result. Specifically, an A1c of 4.5% is not an uncommon sight in these forums. I’ve learned hemolytic anemia is a concern beyond the low end of normal A1c range because excessive turnover in red blood cells can artificially deflate A1c. You might get a lower, better-looking number for a very bad reason.
On the flipside, I see posts like one (now deleted) titled “25F A1C 5.8%, anxious about consuming anything sugar now”. In the body of the post (now inaccessible) I remember the user explaining that they are a very active athlete and they constantly engage in strenuous activity. If you frequent this subreddit, you’ll know that 5.6% is the cutoff for “normal” and that 5.8% falls into the pre-diabetic range, but if you happen to hang around long enough you might run into other insightful articles that can clue you in on exactly why that’s not a real concern. In high-stress environments like competitive team sports, glucocorticoids can temporarily inhibit insulin and strenuous aerobic exercise can trigger glycogenolysis - your body releases stores of glucose for you to use and those levels can stay high for long periods while you’re engaged in health-improving activities, a confusing paradox indeed.
Humans aren’t populations, and lab results aren’t patients. In fact, in medicine there’s a frequent refrain: “Treat the patient, not the lab result” because this kind of absolute-seeming metric can be very misleading if you anchor your treatment around it and disregard other in-range but indicative markers of poor or good health.
I’ve seen this error made over and over and over, but yesterday it really saved me: I got my A1c result back for the 3rd check after my initial diagnosis: my A1c went UP (just barely, perhaps within error) despite continuing to lose weight (now over 100 lbs down), trying very hard to control my blood glucose levels using a continuous glucose monitor (CGM) and only very minor decreases in medication dosage, roughly proportional to weight loss. There’s a couple confounding biometrics in the room with me though: GMI and o2 saturation.
Alongside my increasing A1c (up to 5.7% from 5.6%) my GMI (glucose management indicator, something like an A1c but calculated based on CGM data independent of A1c) remains the same (5.5%) as it did when my A1c was slightly lower. Blood oxygen saturation also continues to trend into a higher, tighter range as the months drag on. It seems intuitive to me that blood oxygen levels will increase with the health of RBCs. I also expect the lifespan of the cells will increase with their health, and with this increase of lifespan glycation will increase without any actual change in average blood glucose levels. I’m almost certain this points to an improvement in overall health superseding any concerns that could be had by taking A1c too seriously.
Anywho, don’t measure yourself against numbers that you can’t explain. That’s a recipe for failure without a path to success. Even aiming for the middle of the range is probably a mistake, as you can see it is for our deleted post’s OP and would be for the athletes spoken about in the article linked above. And as people are reminded so frequently in these subreddits, don’t get your medical advice online and don’t try to diagnose yourself based on numbers alone. Consult your prescriber or care team instead.