HbA1c Explained: What Your Number Really Means

One Number That Summarises Three Months

A fasting sugar tells you about one morning. HbA1c tells you about the last eight to twelve weeks. Glucose in the blood attaches itself to haemoglobin inside red blood cells, and because those cells live about three months, the percentage of “sugar-coated” haemoglobin becomes a running average of your control. That is why it is the number we treat by.

It is also the number most often misread. A good HbA1c does not always mean good control, and a rise of half a percentage point can matter more than patients realise. Understanding what the figure includes — and what it hides — changes how you use it.

What the Ranges Mean

HbA1c is reported as a percentage, and sometimes also in mmol/mol. The diagnostic bands are the same worldwide.

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Roughly, every 1 per cent change in HbA1c corresponds to a 25 to 30 mg/dL change in average glucose. A drop from 9 to 8 per cent is not cosmetic — it measurably reduces the risk of eye, kidney and nerve damage.

Why Your Target Is Personal

Below 7 per cent suits most adults, but it is not a universal goal. We tighten it towards 6.5 per cent for younger people recently diagnosed, where preventing decades of complications is the priority and hypoglycaemia risk is low. We relax it towards 8 per cent for older patients, those living alone, those with heart or kidney disease, and anyone experiencing frequent hypos — because in those situations a low sugar is the more immediate danger.

In pregnancy the targets are stricter still, and are managed alongside diabetes in pregnancy care. A target set once at diagnosis and never revisited is usually the wrong target five years later.

When HbA1c Misleads

The test measures haemoglobin, so anything that changes red blood cell lifespan changes the result — regardless of your sugars.

• Falsely low in anaemia from blood loss, haemolysis, recent transfusion, advanced kidney or liver disease, and in later pregnancy
• Falsely high in iron-deficiency anaemia and vitamin B12 deficiency — both extremely common in India
• Unreliable in sickle cell trait, thalassaemia and other haemoglobin variants, where a different assay or a fructosamine test is needed

There is a second, subtler problem. HbA1c is an average, so it cannot see swings. Someone running 60 mg/dL overnight and 300 mg/dL after meals can produce the same 7 per cent as someone sitting steadily at 150. Their risk is not the same. This is where continuous glucose monitoring earns its place — it shows time-in-range and variability, which HbA1c cannot.

How to Bring the Number Down

Start With the Pattern, Not the Average

Before changing medication, we work out where the excess sugar is coming from. Fasting readings high but post-meal acceptable points to overnight liver output; the reverse points to meal size and composition. Blind dose increases raise hypo risk without fixing the pattern.

The Changes That Move It Most

• Portion control of rice, roti and other refined carbohydrates — the single biggest lever for most Indian patients
• A brisk 30 to 45 minute walk on most days, ideally after the largest meal
• 5 to 7 per cent weight loss, which improves insulin sensitivity across the whole day
• Taking medication at the correct time relative to meals — a surprisingly common reason for a stubborn number
• Treating sleep apnoea, thyroid disease and vitamin deficiencies that quietly worsen control

How Often to Test

Every three months while treatment is being adjusted, and every six months once stable. Testing more often than every eight weeks is pointless — the number physically cannot have caught up yet.

When to See a Diabetologist

Book a review if your HbA1c has risen despite unchanged treatment, if it has stayed above target for more than six months, if it looks good but you are having hypos or feel unwell, or if you have never had your complication screening done. Our diabetes care clinic reviews the pattern behind the number, not just the number.

Conclusion

HbA1c is the best single measure of diabetes control we have, and the strongest predictor of long-term complications. But it is an average, and averages conceal as much as they reveal.

Use it as the headline, then look underneath — at your fasting and post-meal pattern, at your haemoglobin, and at how much time you actually spend in range. That combination is what a treatment plan should be built on.

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