Hemoglobin A1c High: When Your Blood Sugar Test Doesn't Tell the Whole Story
Have you ever gotten an A1c result that just didn't make sense? Maybe you've been eating well, managing your health carefully, but your A1c came back higher than expected. Or perhaps you're dealing with symptoms that suggest blood sugar issues, but your A1c looks perfectly normal.
Here's what I want you to know: A1c has never been the be-all, end-all test we've made it out to be.
As a licensed nutritionist who's spent years helping people hack their blood sugar using continuous glucose monitors, I've seen countless cases where A1c results were misleading—or flat-out wrong. Let me share what every healthcare practitioner and health-conscious person needs to know about when A1c fails us.
⚠️📢Spoiler Alert: Don’t give up on A1c, just understand its limitations.
What Hemoglobin A1c Actually Measures (And Why That Matters)
Before we dive into the problems, let's get clear on what the A1c lab test actually measures.
A1c measures how much sugar has stuck to your red blood cells over the past 3 months. Think of it like this: the higher your blood glucose levels, the more sugar gets stuck to your hemoglobin. Since red blood cells live for approximately 3 months, A1c gives us an indirect measurement of your average glucose levels during a 3 month period.
But here's the catch—anything that affects how long your red blood cells live will affect how accurate your A1C reading is.
This is where things get interesting (and problematic).
Why A1c Was Never Perfect to Begin With
Let me be clear about something: A1c became the standard because it's convenient, not because it's superior. Don’t get me wrong, the convenience factor is great and I want A1c on everyone’s annual lab panel. But let’s take a closer look.
The oral glucose tolerance test (OGTT) was always better at detecting blood sugar problems. But ask anyone who's done an OGTT—you have to fast, drink that awful sugary solution, then sit in a lab for two hours while getting multiple blood draws. It's a big ask.
But hemoglobin A1c? One simple blood draw. Done.
But convenience comes with costs. A1C misses a lot:
It doesn't show the dynamic nature of glucose control
It misses hyperinsulinemia (elevated insulin)
It's late in flagging metabolic syndrome
What to Do When A1c is Elevated: Don't Stop at the Number
When I see an A1C of 5.7 or above, I never treat it as the final answer. Instead, I use that elevated number as a signal to look more closely at the whole metabolic picture.
This is crucial because by the time your A1C hits 5.7, you may have had elevated insulin for years—maybe even a decade. It can be a sign that you have metabolic syndrome.
Better early markers for metabolic dysfunction include:
Increased waist circumference (indicating increased visceral fat)
VAT (visceral fat) from a DEXA scan or Inbody Scale.
Elevated fasting insulin levels
Triglycerides (I look at anything over 100 mg/dL, not the standard 150 mg/dL)
High blood pressure (over 120/80)
On the flip side, you could have an A1c of 5.7 and be just fine. It depends on your glucotype, which is something I’m diving into in my upcoming book, Hack Your Blood Sugar.
When A1C is High and Accurate, but Misleading
Before we get into the inaccuracy issues, there are situations where A1c can be elevated and telling the truth but misleading: This can include periods of illness, inflammation, intense exercise, and certain medications.
During COVID, I was running group programs with people using continuous glucose monitors. I watched person after person with normal fasting blood sugars of 80-90 mg/dl (4.4-5.0 mmol/L) see their levels spike to 140 mg/dl (7.8 mmol/L) or higher for days or weeks during active infections. The same thing happens with influenza or any infection. Your inflammation levels rise, and that naturally raises your glucose levels.
Steroid medications are also notorious for elevating blood sugar. Whether it's a cortisone shot for joint pain or prednisone for inflammation, these medications can significantly raise glucose levels for weeks after your last dose. Just as when we are experiencing stress and our natural corticosteroid levels rise (cortisol), these medications naturally make us more insulin resistant and increase our blood sugar while taking them.
So if someone calls me worried about a suddenly elevated A1c, my first questions are: "Were you sick in the 3 months before that test?" and "Did you receive any steroid treatments during that time?" If yes to either, I tell them to get it retested in 3 more months.
When A1c is Frankly Lying to You
Now let's talk about the situations where A1c is genuinely inaccurate. This comes down to red blood cell lifespan:
🩸Shorter red blood cell lifespan = Falsely LOW A1c
🩸Longer red blood cell lifespan = Falsely HIGH A1c
What’s the most common cause of a longer red blood cell lifespan? Anemia.
Conditions That Cause False LOW A1c Readings
Recovery from acute blood loss (think postpartum or post-surgery)
Hemolytic anemia
Enlarged spleen (which can be completely asymptomatic)
Pregnancy: due to high production of red blood cells
Conditions That Cause False HIGH A1c Readings
Iron deficiency anemia (the most common cause)
Hypothyroidism (lowers red blood cell production)
Chronic kidney disease
The Genetic Factor: Hemoglobinopathies You Need to Know About
Here's something that doesn't get talked about enough: Genetic disorders affecting hemoglobin are the most common inherited single-gene disorders worldwide. Over 7% of pregnant women carry significant variants.
Two main types affect A1c accuracy by causing false LOW A1c readings:
🩸Alpha-thalassemia (common in Southeast Asia)
🩸Beta-thalassemia (common in Mediterranean regions, Italy, Greece, North Africa, and South Asian populations):
We need to keep racial and ethnic differences top of mind when interpreting results.
Red Blood Cell Distribution Width: An Early Warning System
There's a simple lab marker that can tip you off to A1c problems: RDW (Red Blood Cell Distribution Width).
RDW can be an early predictor of anemia and is included in your complete blood count (CBC). When I see elevated RDW associated with higher A1c, it's often showing early anemia causing a false A1C elevation—not actual diabetes.
This is your cue to dig deeper into the blood chemistry.
Low hemoglobin, hematocrit, and/or ferritin can also be indicators of anemia. Below is a picture of a CBC sample report.
Take Charge of Your Lab Game
🧪🩸You don't have to wait around for providers to order the labs you need.
Patient self-ordering options:
JasonHealth.com (through Quest)
Life Extensions (through LabCorp)
Practitioner ordering:
Fullscript/Rupa (Quest only)
Evexia (LabCorp)
Most blood chemistry labs aren't expensive.
A complete blood count (CBC) costs about $5.
An iron panel, including ferritin, is around $13 to check for anemia
A1c is around $7
Important note: If you're self-ordering labs, please make sure you have a qualified practitioner review the results with you. Getting the numbers is one thing—knowing what they mean and how to act on them is another. Don't try to go it alone with lab interpretation!
When You Need Different Tests: Alternatives to A1c
So what happens when you suspect your A1C isn't giving you the full picture? Maybe you have iron deficiency, thyroid issues, or you're from one of those ethnic populations where A1C tends to be less accurate. Maybe you have high insulin keeping your glucose levels down, but causing other problems like metabolic syndrome.
That abnormal A1c result is your sign that you need to take a closer look.
The good news is there are other tests that provide additional information about your blood sugar patterns. Some of these you might want to discuss with your healthcare provider, and others you can explore on your own.
Tests That Look at Shorter Time Periods
Glycated Albumin - This test looks at about 1 month of blood sugar control instead of 3 months. It's especially helpful if you have iron deficiency, kidney disease, or those genetic hemoglobin variants we talked about earlier. Think of it as a "recent snapshot" versus A1C's "long-term average."
Oral Glucose Tolerance Test (OGTT) - This is still considered the gold standard for detecting blood sugar problems. Yes, it's the one where you fast, drink the sugary solution, and sit in the lab for a couple hours getting multiple blood draws. Nobody loves it, but it shows exactly how your body responds to a glucose challenge in real time. You can also order insulin tests at the same timepoints.
Tests That Look at Insulin Function
🩸Fasting Insulin: Ideal range is 3-7uUI/ml
🩸Lipid panel: Here, the triglyceride levels can be helpful. A fasting TG level >110 mg/dL indicate higher insulin levels. Certainly, >150 mg/dL would be more conclusive. Others point to a triglyceride/HDL-Cholesterol ratio over 3.0 being predictive of elevated insulin and metabolic syndrome.
If your insulin levels are elevated, it will tell you that you DO have issues with your blood sugar, and your body is having to produce excessive amounts of insulin to take care of it. Because of this, it looks like your blood glucose is fine (which it is), but a metabolic storm is brewing, and you could be well on your way towards developing metabolic syndrome.
For Practitioners: The Technical Details
If you're a healthcare provider looking to order these tests for your patients, here are the specifics:
Glycated Albumin ($25)
Available through LabCorp/Evexia as "GlycA"
Quest lists it as "glycated hemoglobin/glycated protein" (not yet available through Fullscript but coming soon, I’m told)
Perfect for patients with iron deficiency, kidney disease, or hemoglobinopathies
Oral Glucose Tolerance Test ($15)
Available through most lab companies
Pro tip: Getting it combined with insulin response testing is tricky—you usually have to order a separate test “Insulin Response to Glucose” and coordinate timing with the phlebotomist
Add insulin response test to this for another $27
Insulin Resistance Panel with Score ($82)
Available through Quest/Fullscript
Includes C-peptide and intact insulin
Provides a numerical score—anything >30 suggests insulin resistance
Fasting Insulin ($7)
Available everywhere
Optimal reference range: 3-7uIU/mL
Basic Lipid Panel ($6)
Available everywhere
Reference ranges: TG<110mg/dl, TG/HDL-C: <3
💬 Practitioners, join my free Using CGM in Clinical Practice Facebook Group where we discuss complex cases, share interpretation strategies, and support each other in using CGMs and navigating the metabolic health landscape.
CGM: The Missing Piece of the Puzzle
Continuous glucose monitors (CGM) have revolutionized how we understand blood sugar patterns. But here's what most people don't realize: even CGM data might not show the whole picture if someone has robust insulin production.
This is particularly important for people with conditions like metabolic syndrome who might still be producing plenty of insulin to keep their glucose readings looking normal on a CGM, even while their insulin levels are dangerously high in the background. This is where understanding your particular glucotype will be important. Glucotypes refer to differences in our insulin production and insulin sensivity. It’s becoming increasingly well-recognized that identifying the contributions of insulin is a critical part in predicting diabetes and intervening with the right strategies to avoid diabetes, heart disease, and other chronic health conditions.
That's when we might need additional testing or go "old school" with specific carbohydrate recommendations rather than relying solely on CGM feedback.
Don't get me wrong—CGMs are still incredibly valuable tools. They give you real-time feedback, help you see how different foods affect your body, and can catch patterns that other tests miss. I use them with patients every single day, and they're game-changers for most people. But like A1c, they're one piece of the puzzle, not the whole story. The key is knowing when to look beyond the glucose numbers and dig deeper into what's happening with insulin and overall metabolic health.
The Bottom Line: Think Like a Detective🧐
Here's my takeaway for you: treat A1c like one piece of evidence in a larger investigation.
When you see an abnormal A1C, ask:
Have you (or has this person) been sick recently?
Did you (or they) receive steroid treatments?
Do you (or they) have iron deficiency or thyroid issues?
What's your (or their) ethnic background?
What do other metabolic markers show?
How does CGM data look?
The goal isn't to dismiss A1c or put all your faith in it—it's to interpret it intelligently within the context of the whole picture.
Ready to Dig Deeper?
If you're dealing with confusing A1c results or want to understand your metabolic health better, a continuous glucose monitor can be incredibly revealing. The Dexcom Stelo and Abbott Lingo are now available without a prescription, or you can ask your doctor for a FreeStyle Libre 3+ or Dexcom G7 prescription.
Want personalized guidance on interpreting your data and creating an action plan? That's exactly what I help people with every day. You can download my free guide to getting your first CGM, join the waitlist for my next group program, or set up a discovery call to see if working together makes sense.
Because here's the thing—your health is too important to leave to a single imperfect test. Let's get you the whole picture.
For Healthcare Professionals
Ready to bring this level of blood sugar assessment into your own practice? Join my Using CGM in Clinical Practice Facebook Group where we discuss complex cases, share interpretation strategies, and support each other in using CGMs effectively with patients.
Ready to take control of your blood sugar story? Download my free CGM guide or book a free discovery call to explore working together.
References
Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus: Abbreviated Report of a WHO Consultation. Geneva: World Health Organization; 2011. Annex 1, Some of the factors that influence HbA1c and its measurement. https://www.ncbi.nlm.nih.gov/books/NBK304266/,
American Thyroid Association: https://www.thyroid.org/patient-thyroid-information/ct-for-patients/february-2016/vol-9-issue-2-p-6/
Anantarapu S, Vaikkakara S, Sachan A, Phaneendra BV, Suchitra MM, Reddy AP, Epuri S, Mukka A, Vemvakam D. Effects of thyroid hormone replacement on glycated hemoglobin levels in non diabetic subjects with overt hypothyroidism. Arch Endocrinol Metab. 2015 Dec;59(6):495-500. doi: 10.1590/2359-3997000000065. Epub 2015 Sep 25. PMID: 26421666. https://www.scielo.br/j/aem/a/rsW366cL6jKJps9xX3N4j7k/?lang=en&format=pdf
Laws A, Reaven GM. Evidence for an independent relationship between insulin resistance and fasting plasma HDL-cholesterol, triglyceride and insulin concentrations. J Intern Med. 1992 Jan;231(1):25-30. doi: 10.1111/j.1365-2796.1992.tb00494.x. PMID: 1732395. https://pubmed.ncbi.nlm.nih.gov/1732395/
Riediger ND, Clark K, Lukianchuk V, Roulette J, Bruce S. Fasting triglycerides as a predictor of incident diabetes, insulin resistance and β-cell function in a Canadian First Nation. Int J Circumpolar Health. 2017;76(1):1310444. doi: 10.1080/22423982.2017.1310444. PMID: 28406758; PMCID: PMC5405443. https://pmc.ncbi.nlm.nih.gov/articles/PMC5405443/
Hall H, Perelman D, Breschi A, Limcaoco P, Kellogg R, McLaughlin T, Snyder M. Glucotypes reveal new patterns of glucose dysregulation. PLoS Biol. 2018 Jul 24;16(7):e2005143. doi: 10.1371/journal.pbio.2005143. PMID: 30040822; PMCID: PMC6057684. https://pubmed.ncbi.nlm.nih.gov/30040822/