Getting a blood test result is stressful enough. Getting one that says “prediabetes” can feel like the ground has shifted under your feet. But here is something that far too few doctors, nurses, or even pharmacists will sit down and explain to you, if your blood picture at the same time shows signs of iron deficiency anaemia, specifically low MCV, low haemoglobin, and a high RDW, that HbA1c result may not actually reflect your true blood sugar status at all. Before you overhaul your diet, start obsessing over glucose monitors, or lie awake worrying about diabetes, you deserve to understand what is really going on.
What HbA1c Is Actually Measuring
HbA1c, glycated haemoglobin, is the gold standard test for assessing average blood sugar levels over roughly two to three months. It works by measuring how much glucose has attached itself to the haemoglobin inside your red blood cells. The longer a red blood cell lives, the more glucose it accumulates. Most red blood cells live for around 90 to 120 days, which is why HbA1c is considered such a reliable long-term marker.
But here is where the whole system breaks down: HbA1c is entirely dependent on the behaviour and lifespan of your red blood cells. The moment something is wrong with those red blood cells, their size, their shape, their survival time, the HbA1c reading stops telling you the truth about your blood sugar.
Understanding the Blood Picture: Hypochromic Microcytic Anaemia
When your full blood count shows a low MCV (mean corpuscular volume) and hypochromic red cells, that is the classic pattern of iron deficiency anaemia or, in some populations, thalassaemia trait. The red blood cells are smaller than normal, paler than normal, and structurally compromised.
A high RDW, red cell distribution width, tells you there is a wide variation in the sizes of your red cells. This typically happens when your bone marrow is trying hard to compensate for iron deficiency, churning out new cells while older ones are still circulating. Your blood, in short, is in a state of regenerative chaos.
Now consider what this does to HbA1c. Research published in Diabetes Care has demonstrated that iron deficiency anaemia consistently causes a false elevation of HbA1c levels. When red blood cells are smaller and shorter lived due to iron deficiency, the balance of older and younger cells shifts. Older cells naturally carry more glycated haemoglobin, they have had longer exposure to glucose. If your blood has proportionally more older or structurally abnormal cells, your HbA1c will read artificially higher than your actual blood sugar warrants.
A study in the Journal of Diabetes Investigation found that treating iron deficiency anaemia in patients who had been flagged with elevated HbA1c resulted in significant drops in their HbA1c values, even without any changes to diet or lifestyle. Their blood sugar had never truly been elevated. The test was simply wrong.
Why Ferritin Is the Missing Piece of the Puzzle
This is where ferritin becomes critically important, and where the conversation most often falls silent. Ferritin is the protein your body uses to store iron, and a serum ferritin test is the most sensitive early indicator of iron depletion. The problem is that ferritin is not always included in a standard blood panel. In many healthcare settings, a patient can have a full blood count and an HbA1c run simultaneously, and no one orders a ferritin level at all.
This matters enormously because iron deficiency progresses in stages. In the earliest stage, ferritin drops while haemoglobin and MCV are still within normal range. By the time your MCV is visibly low and your red cells are hypochromic, you are already at a more advanced stage of depletion. But there is a significant window, sometimes months, during which ferritin is quietly falling and the HbA1c is already being affected, yet the full blood count has not yet declared anything obviously abnormal.
According to research published in Clinical Chemistry and Laboratory Medicine, low ferritin levels, even before frank anaemia develops, are associated with elevated HbA1c readings that do not accurately reflect glycaemic control. This means a patient with low to normal haemoglobin, borderline MCV, and depleted ferritin stores could receive a misleading HbA1c result and be incorrectly counselled about their diabetes risk at a very early stage of iron deficiency, before their anaemia is even clinically obvious.
The practical implication of this is significant. If you have been told your HbA1c is slightly elevated and no one has checked your ferritin, you are missing a crucial part of the diagnostic picture. A ferritin level below 30 micrograms per litre is generally considered indicative of depleted iron stores, even when haemoglobin is still holding within the lower end of the normal range. Some researchers argue the threshold should be set higher, around 50 micrograms per litre, to catch early depletion before it starts distorting other test results, including HbA1c.
In populations where dietary iron intake is consistently low, where menstrual blood loss is significant, or where chronic low-grade inflammation suppresses ferritin’s reliability as a marker, this problem is compounded further. Inflammatory conditions can artificially raise ferritin, masking true depletion, which is why interpreting ferritin alongside a C-reactive protein level gives a much clearer picture of what is actually happening in the body.
The Misdiagnosis Risk Is Real, and Global
This is not a rare edge case. Iron deficiency is the most common nutritional deficiency in the world, affecting an estimated two billion people globally according to the World Health Organisation. Women of reproductive age, pregnant women, adolescents, vegetarians, vegans, and people in regions with limited dietary iron are all at elevated risk. Thalassaemia trait, a genetic condition that causes microcytic anaemia without iron deficiency, is prevalent across South Asia, Southeast Asia, the Middle East, the Mediterranean, and sub-Saharan Africa, affecting tens of millions of people.
This is precisely why clinicians in these regions need to be especially careful. According to research in the Annals of Clinical Biochemistry, HbA1c is particularly unreliable in populations with high rates of haemoglobinopathies, yet it continues to be used as a stand-alone diagnostic tool in many low- and middle-income countries where access to alternative tests like fructosamine or continuous glucose monitoring is limited.
Countries with high prevalence of both iron deficiency anaemia and type 2 diabetes risk, including India, Pakistan, Bangladesh, Nigeria, South Africa, Egypt, and the Philippines, face the most significant overlap. A patient in these settings presenting with borderline HbA1c may receive a prediabetes label, be started on lifestyle counselling or metformin, and never be told that their anaemia could have skewed the entire result.
What Should Actually Happen When Both Results Are Abnormal
If your HbA1c comes back in the prediabetes range, typically 5.7% to 6.4% by American Diabetes Association criteria, or 42 to 47 mmol/mol by IFCC standards, and your full blood count simultaneously shows a low MCV, hypochromic red cells, and a raised RDW, a responsible clinician should pause before diagnosing anything.
The appropriate next steps include checking ferritin levels promptly and correcting the underlying anaemia first. Once iron stores are replenished, typically over two to three months of iron supplementation, and red blood cell morphology has normalised, HbA1c should be repeated. According to haematology and endocrinology guidelines, fructosamine testing or continuous glucose monitoring may be used in the interim as they are not affected by red blood cell abnormalities in the same way.
Researchers have proposed that patients with haemoglobin variants or known anaemia should not receive a diabetes diagnosis based on HbA1c alone. At minimum, a confirmatory test using a glucose-based method, such as a fasting plasma glucose or a two-hour oral glucose tolerance test, should be performed before any label is applied.
Why This Gap in Communication Exists
Part of the problem is time. A clinician reviewing results often sees an elevated HbA1c, flags it, and moves on. Connecting it to the anaemia findings on the same blood panel requires an extra step, one that many busy healthcare settings simply do not take.
Another part of the problem is awareness. Many patients globally receive results with very little explanation. A letter arrives, or a portal notification pops up, saying something like “your blood sugar is slightly elevated. please see your doctor.” Without context, most people will assume the worst.
There is also a structural gap in guidelines. While bodies like the American Diabetes Association and the International Diabetes Federation do acknowledge that HbA1c can be unreliable in certain haematological conditions, this caveat does not always make it to the front lines of general practice, particularly in overstretched health systems.
The Bottom Line for You
If you have been told your HbA1c is in the prediabetes range, do not ignore it, but do not panic either, especially if you also have findings consistent with iron deficiency or microcytic anaemia. Ask your doctor or pharmacist directly: could my anaemia or my ferritin levels be affecting this result? Request your full blood count and ferritin results alongside your HbA1c. Ask whether treating the anaemia first, then repeating the test, is an appropriate next step.
A study in PLOS ONE examining patients across multiple continents reinforced what many haematologists have long known, HbA1c should never be interpreted in isolation. It is one data point within a much larger biological picture, and that picture includes the health, shape, lifespan, and iron status of every red blood cell in your body.
You are not just a number on a lab report. And a single, potentially skewed result is not your destiny.
FAQs
Q1. Can iron deficiency anaemia really make my HbA1c look higher than it should be?
Yes, and this is far more common than most people realise. When your red blood cells are smaller, paler, and structurally compromised due to iron deficiency, the HbA1c test loses its reliability. The result can read falsely elevated, pushing you into the prediabetes range, even when your actual blood sugar is perfectly normal.
Q2. What blood tests should I ask for if my HbA1c is borderline?
At minimum, ask for a full blood count, serum ferritin, and C-reactive protein alongside your HbA1c. If your ferritin is low, your MCV is below normal, or your RDW is elevated, your HbA1c result needs to be interpreted with caution and ideally repeated after your iron levels have been corrected.
Q3. What is the difference between fasting glucose and HbA1c, and which is more reliable if I have anaemia?
HbA1c reflects your average blood sugar over two to three months but is heavily influenced by red blood cell health. A fasting plasma glucose or a two-hour oral glucose tolerance test measures blood sugar directly and is not affected by anaemia or iron deficiency. If your blood picture is abnormal, glucose-based testing is a more accurate option.
Q4. How long does it take for HbA1c to normalise after treating iron deficiency?
Typically two to three months, which aligns with the natural lifespan of red blood cells. Once your iron stores are replenished and your red blood cell morphology normalises, a repeat HbA1c should give a much more accurate reading of your true glycaemic status.
Q5. Is this problem more common in certain parts of the world?
Yes. Countries with high rates of iron deficiency anaemia, thalassaemia trait, or both, including India, Pakistan, Bangladesh, Nigeria, Egypt, South Africa, and across Southeast Asia, carry the greatest risk of HbA1c misinterpretation. People in these regions, and diaspora populations globally, should be particularly aware of this issue.
Q6. Can thalassaemia trait also affect my HbA1c?
Absolutely. Thalassaemia trait causes microcytic, hypochromic red cells even without iron deficiency. It produces a very similar blood picture and can distort HbA1c in comparable ways. If you know you carry thalassaemia trait, always inform your doctor before HbA1c is used to assess your diabetes risk.
Call to Action
If this article has made you think twice about a recent blood test result, share it with someone who needs to read it. So many people around the world are walking around with a prediabetes label that may not tell the whole story. and awareness is the first step toward asking the right questions. Bookmark this page, send it to a friend or family member, and always remember: one result is never the full picture. For more evidence-based health content explained in plain language, explore the rest of our articles.
Disclaimer
This article is intended for general informational purposes only and does not constitute medical advice, diagnosis, or treatment. The content is written to support health literacy and should not be used as a substitute for professional medical guidance. If you have received abnormal blood test results or have concerns about your blood sugar or iron levels, please consult a qualified healthcare professional. Individual results and clinical presentations vary, and only a doctor or appropriately trained clinician can interpret your results in the context of your full medical history.
References
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• International Diabetes Federation. IDF Diabetes Atlas. 10th ed. Brussels: IDF; 2021
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